For more direct criminal elements, you can make it difficult enough that its not worth them going through the effort to use the 5$ wrench and wait while you have to fetch the key. Beyond that, you're no worse off than you were versus carrying cash. The only thing electronic cards might have advantage over this is many provide fraud protection which will refund/void fraudulent charges.
I don't think you understand what happens when you defy court orders...
Also, mostly this will be used for tax issues, where guess what, the burden is on you to prove that your income was only X, so the more crypto shit you have the easier it is for the prosecution to say you have millions in crypto currency.
You really think ZCash is the first company to think of hiding assets from the gov't?
The court reference you replied to is saying that the court system protects you from having a state actor use force to take your property before you've had your day in court.
ETA: That said, I don't think you need anonymity for this, so it would apply to any currency you can use as cash and secure with a password. I guess the anonymity just makes it more like physical cash in that nobody can track how much or where you spend/receive it. For tax purposes, it would be no different from cash in terms of ability to work under the table and be called on it or accused of it by the IRS.
If state actors use the 5$ wrench, that's illegal and consequently you have the defense of the courts to counter that behavior. Civil forfeiture is dependent on being able to "prosecute" your stuff, rather than you. So if they can't seize it, they have to go after you directly, which puts the burden of proof on the prosecution to demonstrate that the money is unlawfully possessed. The fundamental principle of the US court system is "innocent until proven guilty", so you don't have to prove what your income is, they have to prove it. You only need to counter their claims.
The US certainly has had cases prosecuting "stuff" where said stuff is cryptocurrency. See "United States v. 178.95842915 Bitcoins" [0], which appears to be a civil forfeiture case [1][2].
[0] https://www.usmarshals.gov/assets/2016/bitcoinauction/index....
[1] https://www.pacermonitor.com/public/case/10752506/United_Sta...
[2] https://docs.justia.com/cases/federal/district-courts/washin...
Imagine the opposite scenario. The government thinks you have millions, but you genuinely do NOT have that money. How do you prove to the government that you are innocent and don't actually have the money.
You can't. You, an innocent person, are indistinguishable from a person who actually DOES have millions hidden away in crytocurrency.