I've never actually had the opportunity to get resale value out of a MacBook, or really out of any Mac. I use them until they have no support, and then they get switched to Linux. I have one 2008 Mini that no longer has a function, but its resale value is pretty minimal. I have a 2010 MacBook Pro whose resale value might be enhanced by a newer battery, but it has a dead SSD anyway. What's an 8GB 2010 MBP worth, anyway? $200, even with a new battery?
Everything from 2011 or later is still running.