I generally think towers and defenses are too fragile as they are. Making them stronger would slow down the early game, but hopefully just that. In the mid game any farmed hero should be able to solo towers, it should just take a bit longer, so enemies can react. That's what the game needs. Slowing down the pace at the early game.
I used to want buybacks but now i think because of rejuvenator its not necessary. Plus saving for buyback is not something that new people will like i think.