"Is the accuracy gain going to be worth it?"
First, as with anything else, there is no guarantee you will obtain any better accuracy at all.
If you mean you want to buy a neck sizer die for a factory rifle I sure haven't seen any positive benefits with any bushing die over a conventional sizer. I have seen/had very good results with Lee's Collet Neck Sizers. So much so that I now have six of them and wouldn't trade any of them for anyone's bushing dies at all!
You didn't mention a seater but no seating die can correct for defective necks. Lee's collets give the straightest sized necks I've experienced in some 40+ years of reloading using a LOT of different dies. With good necks, the Forster seaters, and Redding's copies, are the ONLY seaters worthy of being labeled "BR/Competion Dies" for use in conventional presses. No one else is even close.