Nintendo games in HD are a new experience. I even can't wait for Zelda WWHD, it looks fantastic. This, combined with the tablet interface which is great for surfing the net, navigating menus, watching YouTube etc, good 3rd party support, a decent price and free online make it a great product. It's also significantly more powerful than PS360, just also significantly less powerful than the next systems. You could stick with a PS360, but a lot of support will drop off for them in the coming year, especially from 1st party.
I think Nintendo needs to introduce a game besides NintendoLand that really exploits the Gamepad to make a lot of "casual" gamers interested in picking up the system. But even as it is, it's a great product that will have great games.
PS4 and XBOne are probably "more" of an upgrade than I need right now. At the price (including subscription fees) they approach a quality gaming PC. Right now it seems to me that Wii U makes a great living room console with the best local multiplayer and most exclusive content, while PS4 and XBOne are more like cheap gaming PC's. I'm leaning toward getting a new PC, but I am curious about PS4 - it looks solid.