Powershielding is fine. If anything should be changed it would be it's properties, perhaps more knockback for the powershield? (don't make us Luigi players cry too much).
As for the momentum code, Kupo's preferred code works well, very well, and just feels natural to the game. This is not something I can saw for the past code which affected all characters. Maybe this natural feeling is because I'm used to playing the characters in Melee, but I think it's just because the gameplay is fluid (something Melee got very right). I played all the characters and the only one that was questionable was Sonic (but I suck with him in all forms of Brawl, Dark Sonic should be able to make a better judgment).
I do realize that we have the potential to add momentum to enhance each character, Luigi may or may not benefit much from it for example, but for now, especially given the code space crunch (I'm at 255 lines), I will be sticking with this code.