Several things (note I'm working on doing Zmapper and already get bus data from my Harley (If you have google earth, try http://homepage.mac.com/tz1/.Public/HarleyTelem2.kmz)

Not the track, but my Gear and RPM:



This is with a 5Hz GPS, and not fully interpolating the data.

But let me break some misconceptions and myths.

The location is ACCURATE to only a 2.5-3 meters, but is PRECISE to a much smaller space especially over a very short time when the satellites used aren't changing and all have the same error. Otherwise every fix would swing in and out within the 3 meters. It doesn't. It often moves by a micro degree or two at most.

Also, the speed measurement (actually you can get XYZ velocity vectors on some) is also quite accurate, which you would need for performance.

Accelerometers may help but how accurate (and calibrated) are they? You don't need much for a Wii using it as a game device, but it isn't likely to be precise enough for doing performance work. The chips inside might be capable, but you might need to worry about noise, temperature, etc. if you want it to differentiate between 0.65 and 0.66g instead of just 0.6 and 0.7.