Your Medallion status would potentially qualify you for a Comfort+ upgrade on flight if attached to flight, but that is probably about it. The Mileage Upgrade Award program is only available on revenue fares in certain fare classes and is also no longer available on Delta operated flights with the exception of flights departing from the UK, France, and Ghana. You might see an online seat upgrade (FCM) offer on flight. But these are dynamically priced by DL system and an agent can't generate anything for you if nothing is showing. They can be paid in either cash or miles, but the mileage amount is just based on the cash amount at 1 cent per mile. Generally speaking, you can get 1.2 to 1.3 cents per mile of value on Skymiles awards, so it's not really the best use of Skymiles.