I used to think that, and in some situations I'll still use a Power Amp, but I've found that over the course of the game being able to get to enemies (and moar grenades) faster makes a slightly bigger difference. I can understand going with the Power Amp though, Clusterwtfgrenades buffed with Power Amp IV is pretty sweet. 
I think people tend to underestimate the difference AM III make while playing, since they mostly think of it as "I get to the enemies faster and I grab more grenades". The reality though, in my opinion, is that those are the least important bonuses, possibly. The increase in the
walking speed is at least as essential as the running one. Walking faster allows you to manouver faster and better, and always be in that sweet spot that lets you break los/take soft cover/be close enough for a OHK with a shotgun/be in the right spot to throw that cluster/get out of sync range, and I could go on...
A DrellGod with an AM III and the right fitness evolutions walks so fast that you'll rarely find yourself running at all, in matches. And I think the importance of let's call it micro maneuvering is so crucial that the bonus AM gives through that can hardly ever be overstated.