I have a D5100 and am thinking some of the same questions, though I'm not at the point of deciding yet. I'd probably go for the 7000 series upgrade if budget isn't an issue. The user interface seems to have changed enough from the D5100 (even more so from your D5000) to the D5500 that familiarity with menus and controls isn't a huge reason to stay with the 5000 series. I don't know what the battery situation is, haven't researched things that far yet, but if you have extra D5000 batteries that you'd be able to use with a D5500 but not with a D7200, eBay and Craigslist are your friends.