This happened to me a month or so ago due to an equipment change. I had upgraded shortly after purchase for a nominal fee (about $60, since it was just a short flight from MDW-DTW). After my flight, I submitted a form online to request a refund for the upgrade fee and that I would appreciate any additional consideration being a loyal/frequent Delta flyer. A few weeks later, they issued my refund and nothing more. Perhaps I should have been more direct than simply saying "additional consideration", but it is what it is.