Aftermarket hack to get 128MB on motherboard? I've heard rumors of those. Most only support 16MB. You sure about 128? 
I don't know why Commodore continued to cripple their machines with such poor memory access. No fast mem on the A1200 or CD32, slow access on the A4000/4000T, etc. Oh well, just a few in the long list of dumb decisions. Aside from the finger-slicing case and mediocre airflow the A3000 really seemed like the best of them!
Dave Haynie wrote a nice article a few years back explaining why the A4000 has such a terrible memory interface. I can't remember many of the details, but suffice to say Commodore were unwilling to spend money, and what eventually became the A4000 was essentially a stopgap machine, quickly put together, envisioned as an A3000+.