Yeah, Dragon buff cards (and possibly debuff in muliplayer? No, too annoying or unbalanced) instead of Dragon Skill cards would definitely make Wizard Towers useful. They could occupy a slot on the skill bar as well, to force you between passive skills, active skills, and buffs.
I do still hope for some mechanism to trade/sell unwanted cards at some point.
Of course Dragon buffs that occupy slots on the skill bar are already produced by the Wizard Tower in the form of research upgrades, so these would have to be better or we'd end up with the same situation.
And yes, I'd like a way to get rid of useless cards as well, though part of me thinks the solution here is not to have useless cards. I'd never trade in a Mercenary or good Strategy card no matter what the board situation, if the Wizard Tower and Academy cards were better I'd not trade them in either.
