Of course, you can move to a 64bit OS and still run Cubase 32. And 64. On the same machine (though not at the same time - audio interface).
I still run Cubase 32 cause a number of my plugs were still 32bit, didn’t want to mess with bridging (which uses processor cycles), and didn’t really need the additional RAM - though I have 12G installed.
Running Cubase 64 doesn’t really give you any more processing power - save that afforded by the RAM.
This is changing, though. Old plugs get used less and important ones are mostly 64, now. I may reassess soon.