Preliminary Questions:
Do you have an Xbox 360?
Do you hate/dislike Microsoft?
If the answer is no to the above, you should drop the Wii intentions for 360 and try to get a 360 with the money you have. If the answer is yes to either, then here's my take:
I like my Wii, I've had fun on it, but it's not a system I really feel takes precedence over my PS3 o 360. The only game that's came out on Wii that I've been able to enjoy by myself was Zelda Twilight Princess and even then, it still kind of felt, "Eh". Wii Sports, Wii Play, Cooking Mama, Mario Party 8 are all games I can only enjoy with friends. I didn't like playing Super Paper Mario or whatever it was called and I didn't like Warioware.
To me, the Wii is extremely circumstantial and if you don't have friends over every day, gets really boring after a month. It does have some games on the horizon that are supposed to blow my socks off, but a lot of those titles look "party centric" as well.
Just my opinion, but I'd go Microsoft way and if you can't, get some PS3 games/stuff. But hey, the Wii sells for what you buy it for and if not more, so really you can't go wrong getting a Wii either... IF you can get one.