If you are happy with the existing setup, there will be no real difference. Your NAS is quite capable and if was setup/installed well, it shouldn’t be giving you any issues.
I’d love to sell you a Nucleus+, but it doesn’t sound like you need one.
If you are looking for a new toy related to Roon, I highly recommend a big (12.9") iPad Pro to run Roon. It is a super fun way to experience Roon.