If it's too big and or the geometry isn't to your liking, then you should really look into getting something different.
I was riding a 59cm bicycle with some odd geometry and I changed to a 58cm CAAD9 with a shorter stem, and I've noticed a huge improvement in comfort and distance ridden, as well as a slight increase in speed(very slight).

The motor argument is too trite for me; if you will ride a new bicycle more, then by all means purchase one, regardless of how much it improves your performance.