As cheap as its sound, to level all my spells, I went into level 2 and I killed every one but one guy, and just spammed them, and avoided hitting him. Took me a little bit but easier than trying to do it in level... and I am bulldozer higher level.
Erm. I am reposting this from a user named Luciferoh, his comment was in some of the best comments but it was a bit back, so I thought I might repost it so that others might see it
Money machine before having Rainbow and various hp upgrades: play level 2, The Banana Shire, and queue 1 goblin, 1 healing priest, 1 shieldgolem until you're out of space. Stun the central tower when you can. With 10 units and a single upgrade to max mana, it gave me 2300 Infamy [not counting the gold medal, I achieved it earlier]. I think getting to 10 units upgrade could have been fairly easier if I started doing like this earlier. I tried other approaches, but this one gave me out the most. I hope it helps, initial grinding is awful.
Again this is all Luciferoh's idea. And I think it works great. I would get 5500 easy without most of the aura level ups.
I beat the game.... Did the whole Jeer laugh etc all the things i could on that sound panel than I hit menu and... I didnt get the badge... So like... what?