I would never do it, personally. Nothing against LARPers, I do find it...weird. I prefer pen/paper RPing than full on acting out. I think I find it easier to imagine my character say chopping down an ogre than me wearing foam armor, wielding a foam sword and running around swinging at other people. Easier to picture the fantasy I guess.
I don't see why a PR LARP wouldn't work though, it wouldn't be any different than any other LARP, the only thing though would be that you'd have to have a group play the villains. And then it gets into the fact that are you only going to have one group of rangers, because then you have only a small group of people. Or would you have it be some crazy thing with people making up their own ranger teams and having multiple groups? Also with the villains, it might kinda suck if people want to be like the Power Rangers and thus always win, because then the villains would always end up losing no matter what.
Oh but a funny thought just occured to me. The megazord. It'd be hilarious if the group(we'll go with 5 right now) when they form their megazord, pick up some kinda cut out or something of the pieces of the megazord, and stand close together and hold them up, having to move together as if they were one big megazord. Sorry, couldn't help the funny image.