Hmmm.... I'd say, it depends on who your potential customers are. Me? (and I'm assuming most 'car guys') I'd prefer the way it is, with the new tranny in the trunk. I'd run it for as long as it goes with the current tranny, then install the new used one.....
But then again, I'd never buy a Chevy Spark- or anything with a CVT. And who are we kidding? By the time the current tranny dies...most likely, so will the rest of the car.
On the other hand....selling to the average consumer, I think it would be best to replace the tranny, and not even mention it unless asked- as long as it works perfectly....or use it as a selling point "Has new tranny with only 3K miles on it".
Hmmm...in short, I haven't helped a bit here, have I? I've just stated the obvious. My work is done!
On second thought...maybe just replace it now, 'cause even as a "car guy", I'd be leery if someone unknown to me (or maybe even someone whom I knew) were to say 'Yeah, there's a good tranny in the trunk, dude!".
