Melee would be the best smash game even without L-cancelling and wavedashing. Wavedashing literally is just for faster spacing because running (and stopping) and dodge rolling are so much slower and cover less distance at a slower pace.
As for wavedashing, fun fact: the first game with wavedashing was Tekken 3 I believe, made by *drum roll* Namco Bandai. A Tekken character was in PlayStation All-Stars, and there they could wavedash!
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Wavedashing functioned in a relatively similar way, but worked through a fairly different way.
I'm pretty sure l-cancelling was intentional. It's mentioned on the Smash 64 dojo (as Z-cancelling).
L-cancelled (as Z-cancelling) was on the Japanese and American Smash 64 Dojo, albeit under a different name.
Wavedashing is more of an "exploit." To be more specific, it is a result of an air dodging physics engine to where you can dodge into any direction without any limitations in regards to landing on the ground, which creates a sliding motion if done fast, or can work as a sliding "landing" to jumping (called wavelanding), or even can work as a V-shaped dodging mechanism (V-dodging/dashing/landing).
BTW, automatic L-cancelling/less after air-to-land move lag (for possibly all moves) from what I can tell appears to be in Smash WiiU, based on a few gameplay clips from Smash WiiU that we've seen. That is a good thing IMO, because it can lead to more offense, more combos, and just more purely exciting moments.