Elder-Basilisk said:
A wizard, on the other hand is a different kettle of fish. Since he's unable to spontaneously apply metamagic feats, he can't use ES: Fire or ES: cold to always have a double damage elemental type available to him. ES is only useful to him in a few situations:
1. It enables him to take advantage of DC boosting feats (Bloodline of Fire) or abilities (Elemental Savant's elemental focus)
2. He has advance knowledge of what he will be fighting and can prepare accordingly.
3. He selects ES: sonic because nearly nothing is immune to it so he can prepare all his spells as sonics on the assumption that, seven times out of ten it will be as good as normal spells, and 2.9 times out of ten it will be better. (For the .1 times out of 10 that he's facing a bard, destrachan, or Formian...oh well, there's still Magic Missile).
IIRC, the bonus from Bloodline of fire only applies to sorcerer spells, not wizard spells.
I rate the feat an 8 - very useful and powerful for a sorcerer, but not as useful for a wizard. I did not take the feat for my own fire themed sorceress, instead choosing fire variants of several spells (Cone of Cold became Cone of Fire, Chain Lightning became Fire Chains) since I wanted a character that would be dependent on fire spells and unable to switch to other energy types in a pinch (apart from Magic Missile, which has been proven to be effective enough so far).