So I'm about to load up another batch of ammo for some accuracy testing in my AR and a thought occurred to me:

Do the number of firing cycles that a piece of brass has been put through affect accuracy?

The batch I'm working with is some LC, going into the 4th firing cycle, but not with any particularly heavy loads.  In fact, other than a couple that were culled out due to split necks most of them look really good.  Is there anything to be gained by using virgin brass?

Actually fire formed brass to your chamber should be more accurate than new brass, it really depends on your dies and how much it's sizing the case back down and how much run-out it's introducing to the case neck during sizing and also how much bullet run-out you have after seating.

I use a Sinclair run-out gauge to check my brass after firing and sizing to see how much run-out is in my whole setup, with Redding Type "S" dies I get almost 0 run-out in the necks after sizing and bullet run-out is about the same with most being perfect and some are .001" which isn't bad.

These thing IMO make a bigger difference than any when it come to the brass.

I don't think it is a matter of "accuracy" so much as "consistency".  Brass with the same headstamp and the same number of loadings (even zero loadings) should yield more consistent results than mixed brass and, in the long run, allow you to be more "accurate."  Depending on the kind of shooting you're doing, you may never notice the difference.