I think the difficulty of doing something with a "barely used" pack is one of the problems. Tesla likely can't redeploy it. They don't have a mechanism in place for reselling used packs, as far as I know. So barely used or not, it's going to have to go through some disassembly and recycling process, which is pretty wasteful in resources and time.
I don't know that the difference is $10k worthy, but I do understand that there's a big difference between an undelivered battery pack and a delivered battery pack. Maybe it's something like going to a restaurant. If your server places a dish in front of you and you noodle around in it with your fork, you can't send it back and expect them to give it to another diner.
Actually, that analogy is terrible. But I still think that the fact that someone has used the pack at all makes things very complicated. There is likely to be a day, once the Gigafactory is truly operational, that they can rapidly recycle packs for much cheaper, but we're not living in that time yet.