I would like it if spells included more than just BUFF, DEBUFF, DAMAGE, HEAL.
e.g., most spells fall under the categories above, sanctuary, armor, bless, steelskin etc are all BUFFs that do essentially the same thing. Make you last longer in a fight. Slowness, corrupt armor, blindness, etc are all DEBUFFs that essentially do the same thing, make your opponent easier to kill. Fireball, burning hands, cone of cold, demonshreak, are essentially all DAMAGE spells, and then you've got your HEALs.
This is quite hard, but I can forsee spells such clone doing more than just creating a clone of yourself, what if you could order your clone to keep walking slowly in that direction so if someone was following you down west trade route, you could sneak into Troll Forest and leave your clone walking down the road, then the followed can become the follower.
Basically though I would at least like it if Priest, Mage and Esper all had their own damage spells, their own buffs, their own debuffs, that meant that no class was left out, but that gave a at least a little variation.
One goal should DEFINITELY be to restructure the elemental system. Adding elemental masteries that get better through use would be a great idea. So that if you spend a lot of time casting fireball, you will be better at fire spells, but if you start casting too many ice spells, your fire mastery goes down and your ice mastery goes up. Then, instead of just randomly assigning classes elemental strengths and weaknesses, it could be done through the elemental system.
Let's say characters have a total of 100 points that alter naturally through an elemental system. If I cast only fire spells for a few weeks, I might be able to get my fire mastery up to 90-100, but my ice mastery and spirit and death and whatever else might drop to -20 each. The only way I can improve them would be to use them, at the expense of my fire mastery.
That's just one idea, but the only real way of getting spells interesting is to incorporate elements properly.
