You are definitely barking up the right tree. Cubase cannot access more memory which resuts in white plugin guis etc.
If you really don’t want to use 64bit Cubase, I think you could still bridge 32bit to 32 using Jbridge and open up access to more memorythis way (overcoming single program limit)
NB. It’s many years since I had to deal with 32bit so I wouldn’t like to guarantee this info is completely accurate.