I put it down to the fact that Ebay increasingly takes around 16% for a lot of transactions, including paypal, which means the likelyhood of getting a bargain is less and less.
If you post something which you might get 7-10 quid for, by the time ebay takes £1.50 for a listing with a few pictures, 10% final value fee and 4% on Paypal...you aren't really left with alot.
It makes selling/buying random little bits which you are curious about and which have just turned up not really worth it.