The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.
Just because it is now ignored by our government doesn't make it a tautology. It's still the law of the land; it's just being willfully misinterpreted.
Conceptually, how the Constitution works is as follows. The states inherited the sovereignty and unlimited power of the British parliament. In aggreeing to the Constitution, the states delegated some of that power to the federal government, and agreed to refrain from the exercise of certain other powers. The clauses of the Constitution outline the powers delegated and prohibited. All the 10th amendment says is that anything that hasn't been delegated or prohibited hasn't been delegated or prohibited. Which is tautological.
The mere face of the text cannot support an interpretation that the 10th amendment does anything other than state the obvious. If a federal action is otherwise Constitutional, by virtue of falling into one of the delegations, then it is by definition something that has not been reserved to the state.
As far as I can tell, you only see the Tenth Amendment as a tautology because you take for granted the makeup and principles of the American government. It was not at all a given at the time that the Federal government would leave sovereignity to the states and only exercise certain defined powers. For example, it has largely ceased to do so today, in violation of the Tenth Amendment.
The States battled over the wording of each amendment. Many of the debate texts and the notes from the Founders are still available. How an attorney with the Internet at his fingertips could maintain a contrary delusion is really disturbing to me.
There were no throwaway/meaningless amendments in the Bill of Rights.
The Tenth Amendment means exactly what it says it means. The States barely allowed the Federal Government to have any power under the Articles of Confederation. The Constitution was an effort to allow more power to the Federal Government, but certainly not limitless arbitrary powers... thus the Ninth and Tenth Amendments.
It's ineffectual as a limit on Federal power because other clauses of the Constitution allow for any expansion or contraction of Federal power you could want, and what swings the argument is the legacy of precedent.
And although you are correct that prevailing interpretations of the Constitution allow for arbitrary Federal power, I don't believe that those interpretations are supported by the plain text nor by historical understanding of the Constitution.
Most of the rest of the change in the balance of power has come from the changing nature of the economy. Both the plain text and the early interpretations of the Commerce Power (Gibbons v. Ogden in 1824, a mere 35 years after the ratification of the Constitution) support the modern exercise of federal power. What is different is that in 1789, most people lived on farms, grew their own food, made their own clothes, etc. Very little human activity came within the scope of the commerce power, as broad as that power was defined. Today, just this post involves an interstate electronic transaction. It's nearly impossible to buy clothes that weren't made in a foreign country. Etc. Nearly all activity comes within the scope of federal power because nearly all activity is commercial and either interstate or international in nature.
Take the individual mandate, for example. It was fund to be outside the Commerce Power, but within the Taxing Power. What does the 10th amendment have to say about it? If you read the 10th amendment as saying "Congress shall not infringe on the traditional functions of the states to safeguard health, welfare, and morality" then you might say that the individual mandate violates the 10th amendment because healthcare is a traditionally state function. But that's not what the 10th amendment says. All it says is that action which falls outside the Constitutional delegates is unconstitutional. Well if the individual mandate is within the Taxing power, then it is within one of the Constitutional delegations, and is by definition outside the scope of the 10th amendment.
Basically, federal action can never violate the 10th amendment. Either an exercise of federal power is Constitutional under one of the delegations, or it is not supported by any delegation of federal power and is thus unconstitional for that reason.
Re: the expansion of federal power, it's popular but not necessarily accurate to say it has come at the expense of the Constitution. If you had asked the Framers whether a sale of a product in New York, manufactured and shipped from New Jersey, using a bank transaction with a bank and a payment processor located in San Francisco should fall under the purview of the Commerce Power, they probably would have said "yes, that's interstate commerce." Yet, that's what happens when I go downstairs and buy a Snickers bar at the vending machine with my credit card. There is disagreement on this subject, but in my opinion the expansion of federal power hasn't come at the expense of the Constitution, but has come because much more human activity has come within the scope of federal power as it was already defined.
If the king / Parliament passes a law banning anyone else from warring blue clothing then end of story that's the law.
I'm not making the argument that expansion of power comes at the expense of the Constitution, and I actually think most of the Framers were fine with such expansion. If you read the initial debates and correspondence you get the impression that the major writers saw an expansion of federal government power as desirable for the health of the Republic as a whole but impossible to achieve at the time.
Where the problem comes is where the federal government increases power as regards individuals. I can effectively argue that the shift in power from States to Federal govt. is reasonable and in line with at least some Framer's intent. I cannot make the same argument about individual rights.
So asking "what would the framers have thought about warrentless wiretapping" is a bit misguided, because the framers wrote a document against the assumption that the states were the ones responsible for internal security, and could use their very broad police powers in the process.
Really the question is: are we less free than we used to be? And contrary to popular myth, we reallly aren't. If you're not a white male, you are unarguably freeer than you have ever been in the history of the U.S. Even if you are a white male, you are free from many of the overreaches of state police power that you would have been subject to before the Supreme Court applied the Bill of Rights to the state. And it's at least debatable that internal security measures like warantless wiretapping aren't as extreme as say the Alien and Sedition Acts which were passed less than 10 years after the ratification of the Constitution.
I'm sympathetic to the civil libertarian cause, but when people complain about the erosion of liberties, I have to ask: which ones? First Amendment? First Amendment protections are today the strongest they have ever been. The First Amendment now protects commercial works like video games that in the past might have been seen as outside the scope of First Amendment protection. State-level obscenity laws, libel laws, etc, have been struck down by federal courts. Second Amendment? Until 2010, nothing would have prevented a state like Illinois from banning guns completely--states simply weren't subject to the 2nd amendment at all. Fourth, fifth, sixth amendments? In the 1970's the Supreme Court went on a rampage striking down state practices that they felt violated those amendments. Heck, just in the 2000's, the Supreme Court extended habeas protection to non-citizens in Guantanamo Bay. A hundred years ago, that would have been inconceivable.
PATRIOT is a big one.
The intelligence wiretapping authorization (especially as expanded in 2001 and 2008)
CDA and COPA (which were later overturned, but are great examples of Congress passing inherently unconstitutional laws "for the children")
I guess right now I'm concerned about the potential for more 2A restrictions -- I'm doubtful that the 1994 AWB was constitutional, and wonder if it would hold up under the current court post Heller and McDonald.
CALEA seems to be at odds with the 4th, but apparently not.
DOMA (which I guess was fixed)
Aside from the recent gun rulings, I'd prefer the laws of 1975 I think.
The framers put in the Supremacy Clause in order to effectively limit the sovereignty of the States. Madison and others wanted to go a step farther and add in the negative, but they lost that argument by the vote of one state, the deciding argument being that the Supremacy Clause would allow the Federal government sufficient power to control any State law so egregious as to need federal attention.
They were actually worried about things like that because the Massachusetts State Constitution had failed so completely. As Madison wrote in a 1787 letter to Jefferson, "The mutability of the laws of the States is found to be a serious evil. The injustice of them has been so frequent and so flagrant as to alarm the most stedfast friends of Republicanism"
Re: freedom, I don't think we're particularly less free than we once were, save on the frontiers and most of that is perception, not fact. However, setting precedent for the accepted encroachment of rights, or even the perception thereof, is very dangerous to do on a Federal scale.