My friend had (what I think is) a really spiffy idea. If they gave special buffs/bonuses to each of the minions, it would make them a lot more fun to collect, and actually useful!

These would just be minor things like regen, refresh, str+, movement speed+, exp gain+, seals gain+, etc. The more rare & difficult minions could give higher returns on the buffs to make the effort spent getting it worthwhile.