A couple ideas:
Artifacts for heroes. Small items that you can “equip” on heroes to give them small buffs, such as rings, bracers, necklaces etc. They can be common, rare or legendary. This would allow 3*s to be even more relevant, and negate some of the higher star heroes lesser stats such as low defense or attack.
Builder tokens. A (possibly rare?) reward token from events or special quests that allows you to instantly finish any building or upgrade in progress.
I like the artefacts idea, but I see one potential issue with the builder token. What are players who finished upgrading everything supposed to do with it?
Good point. Perhaps it could also be used to finish training or item creation? Or maybe a trading post (I think someone already suggested this) where you can trade in useless items. Matter of fact the goblin balloon could be tweaked to include this feature.
