Quote Originally Posted by Xerlith View Post
Deep Impact(Ex): Beginning at 3rd level, spells of your chosen element ignore energy resistance up to your caster level and still deal 50% damage to the targets normally immune.
I would suggest making it halve the effectiveness of resistance instead of reducing it by a fixed amount. Otherwise there are some edge cases where having resistance to an element would be better than having immunity to it, which doesn't make sense. For example, suppose I'm 8th caster level and I throw a fire spell doing 20 damage. If my target has resistance to fire 20, they'll take 8 damage. If they have immunity to fire, they'll take 10. That's a situation that probably wouldn't happen a lot but it seems like something that shouldn't happen ever.

Quote Originally Posted by Xerlith View Post
Mastery Of The Element(Ex):At 5th level you learn how to cast your spells more effectively. While applying metamagic feats to the evocation spell of you chosen element, the spell level cost is reduced by one, to a minimum of +0.
Furthermore, you can spontaneously apply the Energy Substitution metamagic feat of your chosen element to any applicable evocation spell you cast without increasing the casting time.
I like it. That's the kind of capstone it's worth losing a caster level and taking all five levels of a prestige class for.

I'm no expert at balancing, but overall I like it. Enough to consider taking it for one of my characters, who's an Uttercold Assault Necromancer having trouble finding an appropriate PrC. I might take out Energy Admixture, though.

You talked in the OP about making evocation spells more useful. One way to do that is let them apply effects other than damage. A fun ability would be to make it so that, if you deal damage using your energy type, the target suffers some minor debuff, maybe even specific to the energy type - e.g., if you successfully damage them with an acid spell, they're sickened for one round, that kind of thing. You'd probably need to make it a 10-level prestige class to fit that in, though.