I don't think any of the SB games make any of the others obsolete. I mean, that's like saying that one Super Mario Bros. game makes the previous ones forgettable, or that we can skip straight to Zelda: TP and be well off never playing OoT, LttP, or even the very first Zelda!
I personally think each Smash game, while very similar in fundamentals, has its own unique flavor. Brawl is one thing, Melee is another. And the original is a different beast as well. I don't see anything wrong with enjoying all three if you care to, and especially if you enjoy the delicate differences!
However... playing SSB on the '64 without an N64 controller... it makes me /cry