Pros: a fresh start, and you can insulate outside walls.

Even if they move out before the end of the lease, they need to freshly mow or clear snow right before move out. 

We replaced termite damaged wood, added new flooring, fresh paint, updated fixtures, filled in an old pool, and painted the exterior trim.

The basement barely has vents, all hopper windows are kept closed during the day and it can’t really get any fresh air coming from outside.

Fresh paint?

Lot easier to just start fresh but some like to give the tenants the choice.  

Here a turnover every 2 years +/- is better because I keep my freshly rehabbed unit in better condition when I get in there and update/cleanup.

When we first bought our rental property, before we switched utilities over to the tenants, we had a tenant that kept the window open for a few hours everyday so her dog could have fresh air in the middle of winter.

You shouldn't keep the home listed and rack up a bunch of days on market while you're doing the updates.If I were you I'd take it off the market completely, do the windows and other updates, and then re-list with a fresh listing and new photos when you're done.

If nothing that has sold has been updated, then I'm assuming they've at least been clean with maybe some fresh paint and new carpet?