Unless you're abusing Persistent Spell, there is a pretty small niche of spells you can actually boost with this. How many long term buffs care about caster level? Enough to spend a feat on?
I think it's quiet nice for
1. longer buff-duration (with +3 CL on h/lvl buffs you end up at CL 21 having 24h buffs or CL 9 + xtend having 24h buffs or CL 5+xtend having buffs that last until you go to sleep). Also there are sometime 10min/lvl buffs that you might want to have 24h a day, that's sometimes a good strategy at higher levels and there it helps a lot.
2. permanent buffs vs. dispel.
3. permanent buff effects. Two examples that are REALLY great: Extract Gift and Hardening.
4. Out-of-combat dispels. Spellcraft 9 is met at level 6 when you still need the +3 to Dispel Magic. Later you need it for Greater Dispel Magic.
5. Out-of-combat object destruction. Hoho.
6. Out-of-combat heals. Although it isn't really strong in here except for the Heal spell, which usually isn't for out-of-combat.
7. If you trick people into thinking you wouldn't kill them so the fight didn't start already.