Arcane Mastery allows me to take 10 on any caster level check, which is mostly used to bypass SR, which when coupled with assay spell resistance, makes my caster level checks my CL+20. Most the spells I want, however, have no SR!
I'm a non-focused conjurer at level 2. (We use spell points with scrolls as rarities. I want to ensure I can cast non-conjurations, too!) The other side of my gestalt is Factotum/Artificer for skill and crafting goodness. This campaign may go epic, but that's a long way off if it happens.
If I took Arcane Mastery, it would most likely be at L12. If I didn't take AM at L12, I'd most likely take Craft Contingent.