What helps for multiplayer is increasing the recruit costs through the advanced options, so something like this might work in sp as well. It has of be added, of course and there's the danger of upsetting the sp-campaign balance.
Re autocast, I think it might make sense for a few abilities, but not all.
E.g. the poisonous rounds of the bazooka troops could be autocast, with some other abilities I'm not so sure, since I'd like to have some control over which unit is targeted.
