Out of curiosity, why would you buy echo fighters for characters youd never play?
I'm a completionist, but also, I'll admit aesthetic changes can make me more interested in a character. I never use Pit, for example, but will use Dark Pit just because I like his victory music a bit more. I'd use "Jigglypuff" more if they add Rowlett as an Echo, & I'd probably main "Sonic" or "Donkey Kong" if they added Metal Sonic/Funky.
Plus, Ken showed Echoes don't have to be 1 :: 0.99, so part of me is hoping for an Echo character that changes enough to be more interesting.