I've been in convos about this a few times recently. The general concensus is that there is a hard buyout going for MPS cards to drive the prices up and try to keep them there. I've heard the cards called "non-reserve list reserve list" cards, since the print run is so restricted. I feel like the cards will only continue to go up in value, particularly the highly played cards, although probably not at the current rate of increase.
Personally I only have 2 and they're for a deck, so they're not going anywhere. If I had spares I'd probably sell them, but it wouldn't be at a discount; I really doubt they're coming back down.