Appropriate, nationalise, reclaim, repossess, seize? Steal, if you like. How does 'easy come, easy go' translate in Latin? Rationalisation is the mantra, and there's a lot more fat yet to be trimmed from this particular calf.
the same family for 1500 years
Ummm, go and check the 'family' tree.
Like the monarchy? Like the notion they embody everything that is great about this country? Like the final dribblings of the formal class structure they represent. Those suffocating aspects of it, yes.
ignore any lessons learned from the past
What did you have in mind? That kings and queens are a really great idea, actually, and have always had the best interests of their subjects at heart?
proof that the monarchy is holding back a constitution
Because a written constitution would have to formalise and quantify the role of the monarchy, either stripping it entirely of any notional influence or giving it genuine power. Conjecture? Perhaps, but no more ridiculous than the assertion that the Queen currently provides a valuable check against the excesses of government, or provides a vital ceremonial role.
I suspect that the Monarchy is very cheap and efficient compared to the Government in general.
I suspect you are right. But that is not a sufficient argument in favour of an unelected, unaccountable monarchy.
There are an amazing number of Marxists around here.
Don't see how that necessarily follows. Still, it could be worse, they could be monarchists.