The core problem with summoning spells is that using them consists entirely of filling up the screen with crap and walking away.As long as this remains true, summoning will not be fun to use. Summon Hydra is the only spell that's actually cool and fun under the current system, and that's because its low duration and high damage make it feel as much like a conjuration as a summon, hence the wonderful nickname Iskenderun's Orb of Hydra.
The summoning caps limit the problem, but they don't actually do much to fix it. They just enforce a stricter composition to the big cloud of crap you put up between yourself and the game. Instead of 8 ice beasts, you get 3 ice beasts, 3 hounds, and 3 scorpions. And honestly, I think less about using summons now, because I no longer have to decide if I should use hounds or imps or ice beasts or scorpions; the caps force me to just summon a couple of each.
Summon Scorpions, however, is hit pretty hard by the cap, which cancels out its primary advantage over other summons, larger numbers.
I've noticed a lot of people have suggest that if you want to play a summoner-style mid-game, you should go Wz and then branch out into summoning, particularly for mummies and felids. Is this a problem that would need to be addressed or just clustering illusion? Call Imp is pretty powerful, and this would give it exclusively to Minor Magic. Messing with Summoner Stats would further encourage choosing Wz.
Call Imp used to be the best spell in the Book of Callings, which basically meant that Wz was as good as Su at the only thing Su does. The cap makes it so that massive spamming of summons requires knowing multiple summoning spells, which addresses at least this particular problem.