Q: do you trade in on older mac all-in-one computers?

This is a user-to-user support forum. Apple has a recycle program where you might receive an Apple gift card for your older Macs. You also might be better off financially to sell them yourself. You can use the "Get a gift card online" in the following link to get an estimate: http://www.apple.com/shop/browse/reuse_and_recycle

Some places to consider outside Apple when you trade in are on my FAQ*:

http://www.macmaps.com/selling.html

* Links to my pages may give me compensation.