I've got the mercury PP&S accelerator, which accepts a max of 32MB onboard.
Surely there were more A3000s and 4000s made than accelerators (as many people in the early to mid 90s were happy to use the onboard 030/040s in those computers).
Even generously estimating that there was one accelerator produced for every two A3000/A4000 computers, a third to half of these accelerators were probably Commodore's unexpandable 3640 and third party ones that had the 32/64MB upper limit (especially the tightly cramped A3000D accelerators). The remaining half could take more RAM (128MB etc.).
This admittedly crude estimate means that for every 4 A3000s/4000s produced, there was only 1 accelerator capable of accepting more than 128 MBs of RAM. Remember, most were produced in the early 90s when this amount of RAM was seen as outrageous.
I still believe there are far more A3000s/4000s surviving and in use than there are accelerators capable of taking 128MB RAM.
So I think a Zorro III RAM board would be useful.