Mindstars boost mind power, not spell power. They're best for psychic or nature classes. If you check the shops in Zigur, you'll find a trainer who can unlock the Mindstar Mastery tree (a similar trainer in Angolwen teaches Staff Combat); arcane classes can't get to Zigur barring shenanigans, so there's rarely a reason for them to use mindstars.
Wyrmics, on the other hand, can use mindstars well enough. The Venom Drake tree is pretty caster-y, being more Mindpower-based than the other trees. You can't dump Strength for Willpower by any means, but going with a hybrid playstyle and taking Superpower... I'd be interested to hear how it turned out.
Huge advantage for Wyrmics is that they start with Fungus unlocked, while every other class needs to go antimagic and kill Urkis first. That alone gives them a ton of staying power. My own first winner was a sword-and-shield regen tank Wyrmic; by the end of the game, only Cleansing Flames, Impending Doom, and Curse of Death could threaten him.
Of course, the ultimate tanky caster is the Oozemancer, but you're nowhere near unlocking that yet, and it can be downright cheesy at times.
Oh, derp. Shows how much I've used Mindstars. :V
I tried to use the venom drake tree, but at least early on it was sorta lame, since the first venom drake skill has along cd and it was the only caster ability I started with. Seems like all the later breaths are based on strength, too, so it'd probably have to be a hybrid, yeah. That was probably my mistake, actually. :3