I wouldn't go as far as buying a Wii soley for Wii Fit, you should definitely take interest in other games to make it worth your buy. The games are pretty monotonous. Since I use it like an exercise machine like you described, I only play 2 or three of the Mii Minigames a day along with a few Strength Training exercises. ( I fail at Yoga ) The whole routine takes about 10 min. The only way I can see myself replaying for FUN is when I show it to a friend who has yet to play it. Other than that, theres not much to keep you coming back other than the desire to be fit. You can also unlock more games by raking up time in your "Fit Bank" this logs how long you play the training games and rewards you with a new one once you hit a certain amount of time. After that its a little "meh"

I haven't used Wii-fit myself but from what I've read there are games that make doing it interesting but it's still a workout and it's still something you have to make yourself do. I wouldn't get a Wii just for Wii-fit because an exercise regime is still an exercise regime and honestly will only be so much fun. Get Wii-fit if you want to work on getting in shape, not for the fun value.

I've been playing the Wii Fit for nearly a month, and I'm only just starting to get tired of it; for the price you pay, you really should be serious about exercising, and you can get a good workout if you keep at it. The games are alright, but I'd rather get my workout over with and play something else.