I would say the secondary market is currently, but buying one at MRSP isn't, if you like the watches of course...
But in any case, Watchco actually made Speedmasters this way as well (along with other models - Baby Ploprof's for example) and none of those command a premium, because people just see them for what they are - a bunch of parts. I don't see any 321 made up from parts with a modern case to be any different.
The SM300 was far more popular, and it's value is driven by that popularity and by the fact that new versions are not entering the market - this has also caused the number of fakes to explode. I still believe that should Omega release this watch again, it won't cause the Watchco prices to rise, even if there are some people who still follow Hodonkey by then...