There are various approaches taken to depicting a rich character, and I like the way they handle Castle best. Because he's not just tossing around cash, but when he sees something totally awesome that he'd use like a laser tag set or onion-chopping goggles or a personalized bulletproof vest or a nice apartment in NYC(which most shows set in the city have but don't provide an excuse for), he'll get it. Nothing overblown, just rich enough to say "Why not?"