Why can we not just have all Smash games to play? There is not a need to ditch certain Smash games in favor of others.
Smash 64 is still an interesting game to play and watch in my opinion. Also, without it, the rest of the games would not exist.
Melee has value as well as a fast-paced game that is difficult to master. Also I would not say that the entire meta of Melee is now static and unchanging; this is the year that aMSa came in 5th place at the largest Melee tournament ever using Yoshi, a character considered to be low tier with little potential by many. Also, I was experimenting with Pichu and may have discovered a 0-death against Fox (not tested against a DI-ing human, so it's not a guarantee).
Although I am personally not a huge fan of Brawl, it still has a place in the community because of its entertainment value. Even though it's not the Smash game the most people agree with, it's a Smash game nonetheless.
Smash 4 still has a developing metagame. It is by no means worthless. Although we can say that Smash 4 is slower than Melee or that it has less tech skills, it still requires a great amount of knowledge to play effectively. I find Smash 4 interesting because many of the game's characters seem viable on at least some level of competitive play. This game should not go anywhere. When it is considered that there are over 2500 possible matchups in this iteration of smash, it can stay interesting for a long time (that is, given that people will make an attempt to use the entire cast, which I believe I am seeing, even if people still gravitate towards high-tiers).
TL;DR Every Smash game deserves to coexist. There is no reason to shun one of them and place it in the corner because of its age, nor is there a reason to not invest time in new releases. With proper care and interest, every Smash game can be interesting to watch, fun to play, and have a deep metagame that requires not only tech skill, but also strategy prediction, and mindgames.
*End lengthy paragraph-style comment*