Implementing more options is a good way to add more depth to the playstyle of all characters, making it possible to play a given character in several different ways. It doesn't even have to violate the simplicity of Smash's control scheme; a different version of a special move that is dependent on meter doesn't require any drastical changes.
I am aware that Smash is unique in the way the percentage system works, making different combos only possible during the exactly right circumstances. However, why can't a meter system be added to that? If, let's say, you want to do a combo and then finish it off with a powerful Super Combo or EX move, then you have to be aware of the opponents percentage, DI possibilities etc. As usual.
This will still distinguish Smash from other fighters, only adding new options that reward knowledgeable players, like any fighter should do, in my opinion.
You are onto something right here: how can meter-gaining oriented gameplay be implemented to a game that isn't based on health, withouth resulting in encouraging camping? On the other hand, how do you prevent camping in the first place? Camping can be quite rewarding in many fighting games (SF4 included) in a low-level play. However, good players usually work around it. And don't forget that camping only takes you that far; a full meter doesn't gurantee a win.
Regarding execution of special moves, I am not sure. I agree that Smash shouldn't have "special commands" like other fighting games. But surely, I don't think it's a problem for a good game designer.