I'd go to any profiles I manage that say "first hand knowledge" or that quote a Familysearch or Ancestry family tree as the sole source, and add good primary sources. Then I'd use the information in those sources to write narrative biographies. I'd also add all brothers and sisters to each person in the tree, then their spouses, adding married names and sourcing them as I go, to ensure it is a tree and not just a twig. I'd also add any categories or stickers that were appropriate to each profile.
Once that is all done and the newly added side-branch relatives' bios are all written, then I'd work on researching brickwall ancestors and also look at the oldest edited profiles I manage to see if I could improve the biography or add anything else such as photos, backgrounds, or update the primary source information (new sources are being released all the time).
Of course if you do all this, you are unlikely to actually come to an end point but if you do find yourself twiddling your thumbs, then you could do some connecting, visit a cemetery and take photos to upload, or join a group and help out.