I'm sure in some future expansion pack we can dive deeply into "subtle" spells. It would be great if you could provide some concrete examples of spells you would like. We're all ears.
You don't have to break new ground here, just mix it up a little. You've played war3/wow right? Maybe throw in some spells inspired by mana burn (saps mana and does damage proportional to that mana), immolation (creates a fire shield around a unit that hurts anything adjacent to it every turn - you could even have this be self-destructive!), mana shield, chain-lightning, magic-mine setting (puts a X invisible traps on the map in random spots), reanimate dead (bring back nearby units as undead to fight for you temporarily), mind control, polymorph (turn a unit into a harmless animal), etc., etc.
Really, just steal cool spells from your favorite games. There isn't that much more you can do that hasn't been done without making the game totally convoluted. Should be easy to pop in some HoMM or WoW and pick your favorite hero's spells to use.
edit: upon further inspection of all your spells, it seems like you really do have an overabundance of single target damage spells that don't do much of interest. Come on Frogboy, lightning strikes have to hit multiple targets - it's one of fantasy's great unwritten rules! An easy easy way to increase the coolness of your spells fast is to combine the ones you have. Combine an ice debuff and an ice bolt - BAM instantly interesting spell. Combine your earth DD spell with the slowing effect spell - BAM another interesting spell.
how about this for a rule of thumb - no spell in the game only does damage without any other effect. Follow that and most people will be happy as clams with your spell selection.
edit #2: sorry based on your other post I think I might know why your spells seem to be relatively simple... is it to make it easier for the AI to deal with? God knows if that's what's needed for a good AI it's a compromise I'll take, but if you can pull this off with cooler, meatier spells that would be awesome!