You're right the sport is more valuable, but an SE can become a Sport with a few bits... however I guess you would need to know that first! and the m-sport seats are pretty hard to get hold of to be fair!
I paid £10k for mine at the start of the year.... Montego Blue Sport with 80k, I see them starting at around £8k now which is a bit gutting and equates to around £300 a month depreciation!
I guess all I'm getting at is there's a few people selling cheap in my opinion, means our cars drop in value anyone anyone trying to sell at a reasonable price will struggle and trade values fall through the floor!