Just an update, I softproofed with some ICC profiles I found online to compare the difference for some of my images. I didn't have very much time because there was a nationwide internet outage right before I had to leave on a cross country trip, so my checks were very limited, but still enough that I could appreciate the difference between the z3100 and z3200.
I grabbed ICC profiles for both printers from Hahnemuhle for their photo rag paper (both reg and ultra smooth). Note I don't actually use those papers, they were simply the first ICC profiles I could find online in the few minutes I had available to do this that were available for both printers.
The ultra smooth did not show a large difference, but the regular photo rag showed a quite a bit. Generally a lot more contrast, detail, and less colour blocking in the reds.
At the same time, the z3200 profile actually showed a loss of gamut in the greens/yellows compared to the z3100. I recall reading something a while ago that indicated that the increased red gamut of the z3200 did not come for free, that there was some coverage lost elsewhere from the z3100 gamut, a bit of a contrast tradeoff. For my images the reds are more important, though I could see a landscape photographer might feel otherwise.
Again, these were rushed comparisons in about 15 mins with only a couple profiles from one paper supplier. I wish I had more time to compare. Also I'm aware that these softproof comparisons are only as good as the quality of the ICC profiles -- a bad profile can make a good printer look bad. I don't know anything about the quality of Hahnemuhle's default profiles, or when they were created (didn't have time to check). I mean their z3100 profile could be very very old and lower quality than their z3200 profile, for example.
Anyhow I'm keeping fingers crossed that the improvement in reds I saw with this quick softproof check is indicative what I will actually get, and that any "loss" in other areas of the gamut are minimal.