Are there any expert/master level utility or must-have spells, that require you to put skill points into magic skills you otherwise wouldn't use? Like having to get water and air to master level in MM7, to get fly and town portal.
All the schools are good, but there are certain spells that almost any parties want:
+Dispel is a very hand catch-all if you think you can survive without your buffs one round (prime expert).
+Identify (Prime expert) saves you lots of money early on, and make it possible to identify stuff on the fly.
+Spirit beacon (Lyod's beacon smaller brother), Prime Master.
+Burning determination (Fire expert) nets you protection against stun,sleep, paralyzis. Must have.
+Stone Armor (Earth expert) grants you armor for your team.
+Eagle eye/whatever grants you +Perception, (Air Expert), which is a must have for perception check secret doors if you don't have a character that is perception-geared.
+Resurrection, Master Light. As it says on the tin.
+Sword of lights (or however it's called), Expert Light, does small damage but the enemy can't block this turn. Stupidly useful for certain kind of enemies.
+Skull Crack (Warfare Expert), says 'no' to enemy abilities. Make fights loleazy.
+Whispering Darkness (Darkness novice) lets you find secrets.
There are secrets EVERYWHERE, which kind of means that any party without a freemage is hard to contemplate.