Then there's wavedashing in SSBM. Its discovery transformed the way the game can be played. And countless other examples like you said.
And that edited Bearbaiting mission is a blast! Sure, there's so much on screen that half the time your lasers don't even show up and having bombs actually hit anything is out of the question, but who cares? The eye candy rules.
But one thing I am wondering: is the collision detection going to be (or even capable of being) revised to allow missions of this sort?