Sure, you can look at the equity of the proposed trade from a monetary standpoint. But if you aren't bonding with the guitar you have, and haven't had any luck selling it outright, I think you may want to think beyond the monetary equity standpoint.
If you have an opportunity to trade for a guitar that is more to your liking, and the value difference isn't completely ridiculous, then why not? Even if there's an inequity in the condition. I mean as long as his hasn't been boogered up, drooled on, or otherwise abused, I wouldn't let that stop me from trading into something I'm going to enjoy more than what I had.
Do the research, find out the value of each, go play it, and if you dig his guitar more than yours, and if you can live with losing the value difference, then pull the trigger.
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