I think it's the 8th gen that'd take the biggest hit. A lot of people are holding on to it and waiting for the X, many didn't like the 9th gen and decided to keep their reborn. At the moment finding a good condition 8th gen is like searching for a unicorn, but soon you'll see a heap of them good and cheap reborns in the market.
I am thinking about selling mine too, it'd be hard to get a good price after X comes out. But the problem is like arkhitekt described, it's not worth the effort.