Just a couple of small ideas for Invokers, though they are pretty stout as it stands.
Enchant weapon/Enchant armor - Make it so that the better you are at the spell, the chance that you can put an effect like "sharp, flaming, ice, burnproof, noremove, etc..." randomly on the weapon as well as the hit/dam bonus that you now get. And of course, small chance but increasing as you gain proficiency in the spell. Same for armor, give it some of those awesome things that various pieces of armor can do. I believe it will make the spell much more viable.
Knock - How about having this open those nifty lockboxes also, just another person that can be around that can open them if they're nice enough.