A couple of other barrels might be worthwhile in case you have to use paint that's smaller or bigger than the infinity is comfortable with.
As Paul said, getting the ACE is a good idea, although I believe you have to send your precious away and won't see it for quite a few weeks.
You could get a new hammer, I believe that LPS sell and fit stainless steel ones, although I've never personally been that bothered by getting a few brass shavings in the gap between the hammer and the exhaust valve, they do no harm and are easily cleaned away.
You're already checking out a stick trigger, so that really exhausts the the easy performance changes.
You can get more extreme modifications to your Angel designed to lower the operating pressure - Bonebrake, etc - but you have to send your marker away for a long time and I don't believe the performance improves enough to compensate for the cost and temporary lack of a marker.
Anything else is cosmetic, including - as mgj pointed out - volumizers on IR3s.