Of the three places listed by the OP, I have only been to the Conrad Rangali. Anyone who goes there and doesn't know that the food is overpriced hasn't done good research in advance. In the thread on that property, there is a link the menus and the fact that a burger is $30 is well advertised.

That being said, my wife and I really enjoyed Vilu and thought that the food at the property overall was very good. So in terms of quality of the food, I can't say my experience matches the OP's. But, then again, I just may not have a very refined palate.

In terms of other hotels where you don't have to eat at their restaurants (99% of the Hilton family hotels), I generally agree with the others here: don't eat at the hotel if you don't have to. That's not just Hilton family hotels in my experience, but all hotel brands. High prices, mediocre quality is the general (but not exclusive) rule.