I have been happily using SMB share to access my Synology file repository from my old Vero 4K and am now wondering whether I should still consider switching to NFS on the Vero 4K+. What are the advantages of NFS vs SMB on OSMC atm?
Well generally NFS is a “native” network protocol for linux based machines. So it has the best support and performance.
But if you have everything connected with Gigabit the lower performance (higher overhead) of SMB can be ignored.
It is all on Gigabit ethernet, and I am tempted to just leave it, unless there are stability issues with SMB.
If it ain’t broke, don’t fix it 
I’d agree. If it works, leave it. I switched to NFS when I was running OSMC on a Pi because it was the only way to get consistent video playback without buffering, and I stuck with it when I got the 4K+ because I didn’t want to rescan my whole library (I’m using native NFS rather than fstab based). But if you’re new 4K+ with gig Ethernet is giving you what you need, going to NFS isn’t going to do anything noticeable for you.