First, I think there should be a "Boost All" option where you use a predetermined amount of gems to boost all applicable units for slightly less than it would cost boosting them all individually.
Second I'd like to suggest being able to apply the selected units you've queued in one barracks to the remaining barracks of the same kind. For example, say I were to queue 4 wizards in the first barracks, I would push a button and 4 wizards would simultaneously be queued into the remaining barracks.
