I frequently see people overstate the "cost of entry" to MFD. It doesn't have to be $10k or anything near it. Digital backs are well made and seem to last and last, so don't fear buying used. Two years ago, a total of $3.5k got me a Mamiya 645AFD and 55-110 AF zoom from KEH, plus a just-serviced 16.7 MP square Kodak Proback 645M from a private ebay seller with a good rep. This was the first of the truly portable DBs - tethering is an option rather than a necessity. I already had a bunch of other low-cost M645 manual focus lenses, and I'm still adding more. Happy as a pig in the proverbial, ever since.
So I'm glad to see the 16MP (actually closer to 17 MP) backs getting the praise they deserve. I like square images and when you think about it, a square crop from my other camera (a Canon 5DII) has lower MP! In 35mm/APS format you have to go to 24MP and above to equal or exceed the MP of a square image from these square backs. There are still only a handful of 24MP 35mm/APS format cameras and only one (the D800) with more than 24MP. And all these sensors have smaller pixels (we keep talking about the "fat" 9 micron pixels for a reason)...and then all but the D800E have an anti-aliasing filter to boot.
If you prefer rectangular images to square ones, substitute any of the 22MP backs for the 16MP ones and the same arguments and advantages apply. (One small difference is that DBs are of 4:3 aspect ratio while 35mm/APS is 3:2).
Now sometimes we 16-22MP MFD users can feel like the poor relations in a place like GetDPI or LuLa, crammed with 40-80MP MFD users...but I prefer to focus on the sensor area than the MP. Sensor area is correlated with how much light you're capturing overall, and how hard your lenses have to work for a given MP count. Again, you have to go to 60MP before you find a back/camera which gives a greater square crop area than the 16MP backs, and 56MP before you find a back/camera which gives a greater overall area than the 22MP ones.
So all this is to say, the P30 you're interested in would be a really nice choice. It's one of the few DBs with microlenses, so it has a genuine extra stop of ISO sensitivity. The P30+ is the same with some tweaks, principally in long exposure ability. If I had a P30+ I'd probably wish for nothing else in MFD; at least out of the current or previous backs on the market, none would suit me better.
Ray