I put a deadly wind Fibur barrel on mine, as well as the Bad Karma bolt and softer paddles as it kept breaking paint. Unfortunately my reg was damaged, which the nice people at Tippmann have replaced for me, so none of these upgrades worked. Haven't had the chance to try it properly yet but I'll let you know after my next walk on.
I had an A5 which was modded to bits, it just ended up being unreliable. Best upgrade I bought was the hammerhead barrel (sniped mix kit from BZ) really helped with range and accuracy.
I'd say if it aint broke..... keep your money for games and paint!
The hammerheads are a cracking barrel. I have one on my sierra and works a treat due to the nice tight rifling.
Another note: the pressure gauge and quick strip pins I've heard from other players are a bit of a god send so may be worth taking a look at them