Like the title says ... how do I clean the surface of the plates of stuck on material? I use mine regularly and it seems that more and more "stuff" is sticking to the bottom plate cover. I got most of the material off, but it is a chore most every time now.

I have to tug at the discs to get em off. Walmart bags, Target bags, etc and small amounts of ldpe recyclable. I always pack those (shipping envelopes, bubble wrap or ldpe rolled foam) inside at a least a couple grocery store bags. Other than that, still working like a champ!
The best things you can do to minimize how much the plastic disks stick to the heating plates, and to clean the inks off, are:
Clean with any lubricant, such as 3-in-1 oil applied to a rag or paper towel, WD40 or Silicone Spray lube (also applied to towel first)
Rubbing 3-in-1 oil into the lower silicone pad will help reduce adhesion, and clean off inks
When choosing the outer plastic bag when making your Obaggo, choose a thicker, higher-density plastic, like a cereal box liner or Amazon prime blue/white shipping envelope
If there are inks on the outer layer, turn it inside out, so the inks are facing inwards
Thanks for the feedback. So glad it's working like a champ!