Is it worth taking the three tiers of Drow enchantment resistance on a PM for the +1 enchantment DCs? It's 6 AP and if I didn't take it I'd get either negative energy conduit, efficient empower (already have maximize), efficient heighten or either of the critical multipliers in PM or AM.

Incidentally, is darkfire at all good? It didn't seem too bad in theory but how does it pan out in practice?