Also they don't tend to favour the upper class there's broad support across ideologies and social class that support them. In fact, the republican movements tend to come from upper classes, well true in New Zealand and Australia anyway (not sure of the other monarchies)
I mean that the monarchs themselves favor the upper class. They are, after all, members of it, and exposed mainly to their issues and their side of things. Europe has a terrible history of a ridiculously unequal and unfair aristocracy.
Also the 'consuming public tax dollars' argument is incorrect. The monarchy of the UK pays net tax-in through a deal the government did with monarchy 300 years ago (in short the UK government earns a tidy profit (about £300m/y) from the management of their estate in exchange for a small stipend each year, consistently renewed every period). The monarchs of other countries also have their estates that pay for them in a similar way (don't count Spain though)
Perhaps the monarchs favour the upper class though this has changed largely for the positive over the past hundred years. I would hardly say that today it is an unfair aristocracy, though.
On the democracy argument, there have been multiple referendums to put in place a republic but they don't go through.
So I do agree that the monarchy has some influence on the Commonwealth, more than just having "the right to be consulted, to encourage and to warn".
I've heard the argument that royalty is a net gain in taxes. My point was that they aren't universally popular and there are movements to remove them. Anyway the fact they own lots of land is silly, since it was inherited from centuries ago, when it was originally taken by force. There is nothing stopping the government from cutting them off and continuing to use their land.
It's hard to argue using the popularity argument. In Britain, Canada, Australia and New Zealand the monarch is near universally popular.
The argument for a sovereign head of state is a complex one, the Queen isn't considered as an ordinary family inheriting a lot, its a family which is essentially the head of state and the 'inheritance' goes towards running the country and the benefit of all.
I would understand the disdain from an American perspective, but there's a lot more to it than what is conveyed - the constitutional monarchy system of today isn't like the one 300 years ago, its a wonderful system - to many better than the US system of government, admittedly myself included (I'm an American Politics major if you think there's any bias).
Keep in mind the monarch is there by choice - through democratic vote. As for Australia the 1999 referendum wasn't the first one of its sort either.