I don't remember it ever being taken seriously, that's part of the reason I ended up jumping ship (and regrettably, not taking up competitive Melee). If anything it held the entire Smash scene back because it divided up the player base. It was after Brawl died and Melee was coming back around that Smash started building up to the point it's at now. At least from what I remember.
64 was always that extra-hardcore game on the side where people would try and fail to beat sandbagging Isai.
Ug, man where are you getting this stuff from? You don't have tourneys with 100+ people in them with contestants traveling from all over the world if your scene isn't taken seriously. If you mean there was/is a dedicated group of people who spit ill will and malice towards Brawl and the people who play it, then sure that has been around since the beginning.
And I hear this a lot but Brawl didn't split the community. Melee fan's reaction to Brawl split the community. I don't know know why a game would take the blame for people choosing to treat each other poorly enough to the point where divisions happened.