All three of your ideas sound like they would work to me, especially the idea of traps (though they could devolve into being just another damage delivery system).
I would also throw in that you could have enemies with significant amounts of HP, or mixed companies that include enemies on whom pure physical damage would not be very effective without a utility spell involved. You could also include goals beyond just killing enemies: use spell X on an enemy for a chance at getting a special item, or spell Y to influence the story or have some impact on a later battle (illness, bad luck, madness, etc.).
On a broader design level, what kind of emphasis do you want utility spells to have? Dealing damage is something that can be applied against all enemies in all battles and so it gets a lot of emphasis. Support spells are just that: support. They aren't intended to be a main feature of your force but instead supplement your other characters, and they consequently are of limited usefulness. Do you want to require, explicitly or implicitly, that players have a utility spellcaster in every battle?
SRPGs tend to be focused on killing enemies in the field, but that often isn't the only element-- do you have any notable mechanics outside of battle that spells might be able to influence?