I didn't feel like sifting through this entire thread before posting, so excuse repetitiveness.
I still play Melee pretty regularly. Well, depending on how often I see my step brothers, as they're my main source of competition. I don't play alone very often, though I should to keep my skills fresh.
The question: Is Melee worth playing? Well, that depends. Do you already own it? If so, then why the hell not? Would be a suitable way to spend the time until Brawl if you don't have the money to blow on other Wii titles this holiday.
If you don't own the game, it depends on how much you can get a fresh copy for. I think it might be Player's Choice'd for 20 bucks these days, which is an excellent buy as this is still easily the Gamecube's best game and still sports some of the best character graphics I've seen. Heck, I'd almost say it's still worth a 50 dollar price tag...
And you can't go wrong with practice. It's been said that a lot of characters are offering different feels in Brawl, but if you equally practice with every character, then I can't see it being very disorienting. Press reports have said that if you're familiar with Melee that you can pick up veterans extremely easily anyway.
The choice to continue using the same controller is a good strong reason to continue practicing, too.