Just look at the wii u games if there's like 2 or more games that you would like then, I would say buy it. Also you cant go wrong with both.
Well, I already bought nsmbwu cheap. I just can't play it yet, lol. But a second game that appeals to me, mmm... I don't know. I can see there are great games for it, but I own a ps 3 and xbox 360 as well.
Get both. Just make sure to buy them at a price you are comfortable, many people aren't too pleased with a $300 WiiU that doesn't have a big library right now. Don't make that mistake for the WiiU if that is an issue for you, and don't make it for the PS4 either.