Speedy Girls - Dream Team

Easy way to grind the required parts to upgrade:
Click "Play" and use the bombs on the bottom to smash as much parts as possible, then click Garage and repeat.
That way you don't have to play long games over and over again. It still takes some time though.
Also 100% max stats are not required. Getting all stats as high as possible until it pops is enough (will pop at 90% each appr.).