I've used a custom vanson two piece for 14 years (off and on) worth of track days including two get-offs. It still looks new in most regards. It was fitted as if a race suit, so worked well on the track. Only this year am I getting a new one piece suit made.
I think it depends on what kind of two piece you are using. Compare what you have in person to typical high quality 1 piece suits, and then make an honest assessment for yourself whether you think it offers adequate protection for your body.
May be implicit, but if your jacket has a built in back protector, you should also consider yanking that in favor of one with better coverage (eg longer to protect your tailbone). Chest protectors are also a good idea, and I see a lot more folks using them at the track
Have fun!
B