Haha, well a silver dollar would eat those plants anyways.
That's too bad, but yea, don't want to put anything you can't QT with Sparky, I can't imagine treating the poor guy, scaleless, he's probably sensitive to like everything.
If you found something healthier you could try QT'ing it in Sparky's summer home (if that's not in use anymore).
I think if you posted an ad on craigslist saying you wanted some larger fish you'd get a lot of offers, just gotta find one that'll fit the tank. But, that could be a pain to do as well. "Want a pleco?" "Want a pleco?" Every day.