The popular notion an aluminum driveshaft frees up some measurable horsepower is a myth. The driveshaft is not large enough diameter, is not heavy enough, nor does it constantly change rotational speed to be any significant advantage for the price.
The return on weight savings is almost the same as shaving twice the weight off the car's mass. So if you dropped from 20 lbs to ten, the effect would be around the same as lightening the car by 2 times 10 = 20 lbs.
I've spent about $45,000 on my current project car, and have yet to consider driveshaft weight. As a matter of fact, I ran an 8 second Mustang and never changed to an aluminum shaft.
Now if I had a light weight road race car that needed instant tire speed control when sliding, I'd use an aluminum shaft in a heartbeat.