I'd say you need to look at the list of 3DS games and figure out how many of them you're actually interested in playing. I would still kind of like a Wii since I'm a big Zelda fan, but aside from Skyward Sword, and Metroid Prime 3, there are maybe only a couple of games I'm even moderately interested in, so it wouldn't really make a lot of sense to get a Wii in my case.
So, hit a couple of review sites like IGN and GameSpot, and look over the 3DS games in the genres you like to play. If there are a number of well reviewed games that sound good to you, then I'd say by all means get a 3DS XL, otherwise you'd just be trading a lack of interesting games for the Vita for a lack of interesting games for the 3DS XL.