That's mainly personal preference.
One thing I will say is that people won't react positively to uploading multiple versions of the same map to the workshop.
Typically, people will only make a separate workshop page for the same map if they've changed the gamemode or visual style.
The rule I personally adhere to is "Would I need to design a new thumbnail image for this? If so, it deserves a different workshop page."
Also, remember that you can always download any old version of the map if you're using the "Post an update" system on tf2maps.net, so if you're worried about losing the old version, you should upload it here and post the new version as an update to that.