No credit card required
Browse credit cards from a variety of issuers to see if there's a better card for you.
I wouldnt PC it to a gold, if you want the gold apply for it with the 50 K MR SUB.
I would PC this to a non AF card so that you can keep the history on it.
Ok, in that case I'd axe it. OP has a very healthy credit score, the card will remain for 10 years in the history, I don't think it's going to have much of a long term negative impact.
Whatever you decide to do, don't close the green card until you transfer your 26k MR points or open another MR card (Gold, ED, EDP)!
Depending on your spend, I too would suggest obtaining a new Gold card for the 50k SUB. Depending on which airlines you fly, you can obtain gift cards for the $100 airline credit if you don't plan on flying for that calendar year and use them later. Are you able to use the $120 dining credit made available with this card?
The ED/EDP would be good if you can use the bonus categories, or if not, just to maintain your MR balance. The ED/EDP doesn't really fit my spend well because my grocery spend tends to mainly go to Target, which doesn't fit into AMEX's grocery category. I mainly purchase gas at Costco, which only accepts VISA. I don't have enough AMEX bonus spend transactions to warrant either one of them.
If you can utilize your MR balance or transfer it to a airline program, you might be better off obtaining cash back cards as mentioned in others posts. These are a lot easier to manage rewards, they just tend not to be as lucrative as transfer points programs for travelers.
I wouldn't worry about your credit score. Any impact to your score for closing your account or even opening a few news ones will be minimal, and won't make any difference to lenders when you're talking about 800+ scores.
Figure out what kind of rewards cards benefit you most, and go after those; then ditch the green.