Thanks for the tip. I gave chat a try, and they denied me at first b/c they weren't looking at the price after GCU...saying the price was the same ($39.99 [after GCU and trade coupon] and $39.99). After I asked again and explained GCU, they said they would process the refund. I'm assuming for $8 since I had to do the math for them, and they didn't confirm the dollar amount.
CSR closed the chat window pretty quickly after printing out the formal end of chat lines....not really too optimistic since I've had price adjustments denied before (technically the rep is just agreeing to process a refund request for approval by another department).
I told them:
"I bought it on day one at $59.99, which is $47.99 after Gamers Club. Today it is $39.99, or $31.99 after GC. So $47.99 - $31.99 is $16 which should be my refund amount? I also used a $10 trade-in credit, which you'll see on my receipt."
"That's awesome! You are eligible. Refund processed for $16 plus taxes"
Of course it took a little longer and a bit more "verification" than that, but that was the gist of it.
Total out of pocket ended up being $23.99, since they originally took the $10 off coupon first, before GCU, which is scummy, but oh well. I lose out on $2, but I got rid of Destiny (the first one) for $10. So it's a win.