One guy we spoke to had a Tyros 4 and wanted to PX it in for an Audya, the problem is it will only sell for around £2500 even with the correct Yamaha stand and speakers which is what he was offered against an Audya, but his keyboard still has a RRP over £4000 so it wasn't enough for him and he is going to try and sell it himself. We took a few P/X's to the last exhibition to move on: two Tyros 3 priced at £1599 including Yamaha stand and Yamaha speakers and there was absolutely no interest at all, we also had a Tyros II for £995 with Yamaha speakers which we let go for £820 in the end just to get shot of the thing. So your both very right, devaluation is a very real issue.

We will stick them on ebay just to clear them as normal, but as a retailer its really hard to get back what people want in p/x, plus you have to repair and guarantee the things.

Audya come up rarely for sale second hand in the UK as most go to pro players, but when they do come up on ebay they sell between £2500 and £3000 depending on how well the listing is put together. There are a couple on there at the moment but the seller looks a bit dubious, I doubt I would trust him with a few thousand of my pounds. (disclaimer: this is my personal opinion based on the feeling i get from the listing and his hidden feedback, he maybe perfectly trustworthy)