Welcome to FT, funkfish!

Another consideration you have is whether to keep the Amex Plat or switch to Delta Reserve or keep both. I think you only need one, no sense shelling out twice as much in annual fees. If you are committed to Delta, then Reserve makes sense, you'll get the ton of MQMs and an annual companion certificate and free bags. But if you are going to fly other airlines, the Plat card is more flexible, since, as you have now, Membership Rewards is a multi-airline benefit, gives you lounge access for non-Delta flights, and offers the Precheck/GE credit and airline fees credit. That Reserve companion cert can be worth a lot more than the Plat card benefits, tho.

Tho Membership Rewards has broader and more flexible travel benefits, if you are switching to Reserve, you'll get the signup bonus of 10K MQMs, which will help you towards Plat Medallion status this year (as you recognize) and slightly better upgrade odds. Gold is no lottery ticket, but definitely a noticeable improvement over FO. Feel free to update us on your travel patterns, and stick around!