This is speculation on my part, but I suspect that right now, those trade in numbers are getting lower over time. Not that the offer made specifically to MAPC or other individuals are getting smaller, but I have a hunch (no inside source - just a hunch based on how markets work) that the offers Tesla makes on Roadsters a month from now will be no better than the ones currently extended, and I suspect they will be lower than the offers being extended right now.
My rationale has to do with the size of the market to acquire a Roadster (it exists, but it doesn't seem like it will ever be "big" or "robust" - it's the nature of a small, exotic, sports car), the usability limitations of the car, and most importantly - the number of Roadsters that are currently available for sale.
My own entirely ad hoc and unscientific view of the Roadster market is that something like 1-5 Roadsters sell on a monthly basis. If there are 3-7 Roadsters available, then life works well all around - buyers find cars, sellers find a buyer. With more like 10-20 posted right now, an unknown number of sellers who haven't initiated the sales process, and an unknown number of Roadsters in Tesla's inventory for (eventual) resale, there may be more like 6-12 months of Roadster inventory available right now. It's good of Tesla to act as a market maker and ensure that cars can always move at some price, but with more and more Roadsters accumulating, Tesla (IMHO) are pretty much forced to lower what they offer over time, until the backlog starts getting worked off.
It's the nature of a high level of supply in a market, with a steady demand.
If anybody sees the state of things differently, or with a different nuance, I'd love to hear what I've missed and/or how I'm wrong.