To me, the big benefits of the manual vs. power windows are:

* Much less weight (power window motors are heavy), which saves gas and improves performance;

Actually, I've seen several cars that were bought by street racers. I knew one fellow who as w=also an engineer for Ford and when he ordered his Olds, he specifically ordered power windows as the electric windows were lighter than the mechanical regulator as the motor was stronger than your arm so it didn't need as much leverage.
I suppose they've downsized/lightened 'em some. The ones I've dealt with ('70s-era) were pretty beefy...