I'll second all the others that say not to pay for the vacation. It just sets the stage for expectations and hurt feelings later. If you want to pay for stuff then I'd do paying for a surprise dinner here and there or discreetly paying for a portion of the rental house and saying you got a really good deal on it this year.
I do resent expectations and work hard to prevent that. DH has a harder time not saying yes to every little thing. My FIl is an expert at showing up at DH's work the day before a bill is due with a sob story. All it took was that one time where we "loaned" him money and then he started asking more and more. BIl used to do this as well before DH finally realized he was just being used. We do make good money but our family, DH, I and our kids come first.