Simple, Melee is a classic game and if it were bought now would be a great thing to tide you over till Brawl. You can compare the difference between that and the new one. Play as your favourite characters from the past game that may not be in the one etc. I could keep going but I won't.
Thats why though you should get Melee and the other games mentioned.
Don't overlook what the Gamecube had to offer us.