You've got the right idea- this old stuff has VALUE! You'd be amazed what people pay on eBay for what we consider "heavy crap". My whisperlite stove with pots- $40, old North Face bag $75, Sierra Designs tent $125, worn-out Gregory trad pack $50...I could go on and on! My brother once sold his worn out running shoes on eBay for $20! Basically, if you post it, especially backpacking stuff, it sells.
When using eBay, you exchange $ with PayPal- quick and easy. I've had close to 200 transactions and have only 1 bad experience. It takes a while to get it down but once you do, it is great.
With a baby at home, I don't have the cash for lots of new gear. With eBay, I stick with "lateral trades". :-)
Worth checking out!