Well I got bored today and that's always dangerous. Anyway i may be adding this to the parts list
https://www.sparkfun.com/products/9802 why well by adding in an SD card slot you get the ability to log data you can also store data even without power or without using the arduino's built in memory. But if we log data you can also do things like create Speed to MPG charts Or Speed to RPM charts even monitor the throttle position. So even though it adds about 15 dollars I feel it's quite worth especially since it adds in a feature that both the scangauge and ultragauge don't have.