All above good ideas..note the old world file will need a bit (ok a lot !! ) of time to rewrite the new features into your world file ..as pointed out by those above.. having explored areas means there will be NO new content in those locations.. personally i know i missed out on quite a few ice caves due to running thru nearby mountains :-( so its a personal balance between old world buildings and new world advantages and materials :-) but since its NOV 2021 ... id start again...maybe load your character up with stuff before you transit :-)