Thanks so much for your reply. I'm looking to pay for the upgrade. Any idea what these gate upgrades usually cost? I've seen a couple figures in various threads that make me wonder if it might be worthwhile to just call JetBlue and ask them if they'll return the points and let me pay for the Mint seat as a rebook, hoping of course they'd waive change fees.
One more question for future knowledge, if you're on a paid ticket and looking to buy a paid upgrade, do you upgrade at the gate or are there checkin/kiosk options?