Did you play melee competitively? Just wondering, really. Thinks like multishining edgeguards or shinebairs with fox (just 2 quick example) and certain techniques required such precision it really was hard to maintain the level of caliber without practice. Sure the main things like L-cancelling and all was easy to come in and do without practice, but the real high level gameplay was hard to keep up without practice.
Yes. You can in any game. The reason people may do badly in melee now is because the look is kind of the same, but their minds play like it's Brawl now. Remember when Brawl came out and it took forever to kill people for the most part? (Doubt our Olimar mainers felt that way, but people who were picking Marth, fox, falco, shiek for a little while surely felt differences).
Same thing. The tech skill doesn't go away much. However, when we pick it up (Say, if we lived close to eachother and you are like "Show me then", it would take a couple matches just like Dabuz's friend took. Maybe more, yes, because there are techs and whatnot to remember how to do.. but yeah, same thing. WC3, Online games, chess, sports (Unless you became unfit), it's really all the same. Muscle memory or past memories really.
To answer your other question, yes, I played competitively, however at the time I didn't drive around and had more stuff to do. Now that Brawl is out, I enjoy the game again so I can play it competitively and drive long distances for the game I guess.
Summary- Yes I played. Yes, it should be as easy as not riding a bike for years and trying again.