I am starting to feel pretty confident that many people on here haven't watched Palmer at all this year. In our current situation we would be trading Sherman and getting a worse kick. Palmer was recovering from injury sure but he went backwards a long way this year and was dropped three times (note I haven't checked causation of each on - may have been injured ). His kicking is terrible, he was not the accumlator he was when he was no longer the focus and he dropped off as a goal scoring threat. Having him as the centre piece of any trade is highly overvaluing his trade worth. Its like valuing Sherman based on last year rather than this year.
I would include Palmer for a couple of reasons.
He has shown he can perform at AFL level. 2008 was a good year. Yes his disposal was below average but him accumulating and handballing to Rich wouldn't be such a bad thing.
Came off a compromised pre season this year as you mentioned. This was effectively his second season of AFL after missing the majority of last year with the knee. He would have struggled with confidence and expecting him to set the world on fire off a short run is not fair. It would have been a big ask to come back and replicate the form he had shown pre injury immediately.
Freo would IMO entertain the prospect of including him in a Clark trade. There are a couple of more promising younger players on their list but they won't be accessible.
I admit we would be losing out slightly as Palmer + a later first rounder (or a Suban/Ibbotson) would be a loss for us. But if Clark is leaving next year regardless we may end up worse off. He is still young and could easily recapture the form that won him the Rising Star. At the very least he has some scope for improvement and the potential to be a very solid player.
Again though, if this is just a rumour, I would obviously much prefer to keep Clark as he adds more to our side. Just need to plan for the worst case scenario