Seats are nicer, the wheels are nicer, the colour is nicer, is does not suffer from lag< hesitation> bad fuel maps, gets better mileage, the sound is better on the stereo.
If the MP3 was not my wifes...I would have turbo'd that instead of buying the MSP....the MSP is nice and when/if Mazda fixes the ecu issues it will be fine. We have a CAI in the MP3 and it sounds nice.