Canon EOS 20d advice

Two questions:
First if I go to local camera shop like Ritz, do they usually take
trade ins? I'm thinking of trading up from a EOS 20d up to a 40d
(body only of each).

Assuming it can be traded in, what is the trade in value of an EOS 20d
body (excellent condition) today? If I should sell it myself, what
would that value be? And do they only take trades if you buy a new
one from them?

Off topic, for a typical home user, is the 40d worth upgrading from
the 20d? Will the pictures taken by the 40d be noticeably better to
the eye than the 20d? I suppose value wise I'm better to stay with
the 20d since its paid for but I'm willing to cough up say $500 more
if the 40d is worth upgrading for. I assume the lenses and the shoe
for the flash on top is the same for both models?
Suggestions/advice ?