I love my GT, but if you don't care for the HIDs, auto wipers, and the Bose system, you should definitely save $$ and go with the sport.
Bose system is all right, but it's no Mark Levinson. It's not as good as my Alpine system in my RSX; nevertheless, as factory systems go, its sound should satisfy most people. (no mp3 CDs >_<) So... like the others have said, you should think of it as a small extra, but your decision shouldn't be based on the stereo.
Rain-sensing wipers are simply awesome, and they really do work great. I think it should be the standard feature on all cars in the market.
I also like the HIDs. Sure, it looks nice, but being able to see much better at night is such a benefit especially for a car like the MS3 (zoom- zoom!). IMO, aftermarket HIDs don't perform well compared to the OEMs. (not to mention it's illegal).
The trip computer (correct me if Sport has it, too) is dumb. Its fuel calculations are always off by like 2mpg (so much for its "computing" accuracy), and the live-fuel consumption display is just silly. Will I really get 99.9 mpg while coasting in 6th gear? I think not. ^_^
Again, I like my GT, but if you couldn't care less about those things, go with the sport. Hope this helps. *^_^*