Actually, I believe that the Curve upgrade modifies the aura around your paddle. It grows more curved. The Width upgrade only affects the width you get from the 'Bigger Paddle' upgrade, I think. And yes, I believe the Powerup upgrade is the least efficient compared to the other two.
Say, can there only be one 'stack' using cover at a time? For example, can you put 5 machineguns behind a wall at once? =O I notice the Germans seem to be able to do that. >_>
Time for some math! SR(small room) x RG(rebound gun) = PWN(age). Got to 5820 points this way. ^^ I never really got the point of the shotgun and Glock - They both seemed like you needed to get close to really do anything.