Grim is once again correct 
I currently place the VST dlls in C:\Program FIles\Common Files\VST2, which mirrors the VST3 path (C:\Program FIles\Common Files\VST3). In the image, how it is organised internally, pretty similar to what Grim recommended.
You can use the same structure for 32 bit plug-ins for consistency in the same path for 32 bit plug-ins (C:\Program FIles (x86)\Common Files\VST2).
All plug-ins are shared between C6.5, 7.5 and 8 here.
We have articles, if you want to check them out
https://www.steinberg.net/nc/en/support/knowledgebase_new/show_details/kb_show/using-32-bit-plug-ins-on-64-bit-systems.html
https://www.steinberg.net/nc/en/support/knowledgebase_new/show_details/kb_show/instructions-on-how-to-organise-32-and-64-bit-plug-ins-separately.html
