One thing that heavily influences it being under or overpowered is how often it can be used.
I mean, being able to do +50 damage 1/day vs. being able to do +5 damage on all attack rolls...I'd generally be more worried about the latter.
I'd give a better answer if I knew from memory what exactly is required for circle magic, so I'll update this later. But that's something to be remembered regardless of how beneficial it is to have it when it can be used.
Well, with circle magic, the only real limit on how much it can be used is practicality. The ritual takes an hour per shot, and requires casters other than you to step in and each cast a spell. You can boost caster level, and apply empower, maximize, and/or heighten to spells without increasing spell level, but these are all limited by the total spell levels from your buddies.
The way I see it, practicality imposes a limit here, since I doubt a party will want to devote the number of hours waiting for the caster to really jack things up with it, and PC casters wouldn't likely want to use vary many powerful spell slots for that, and NPC casters tend to have more limited ability to contribute.
Also, I was considering scrapping Tattoo Focus and using Spell Focus in its place, since aside from qualifying for Red Wizard, they do basically the same thing.
