You should be able to simply copy the contents of your old c:\vst folder to the new location and run Plugin Manager (after entering the new path in Plugin Manager, of course). PM will take care of the registry.
But if you want to reorganize the directory structure, be careful that any data folders keep the same relationship in the file system to their plugin DLL. For example, Dim Pro (and many other synths) expects to find its samples in a subdirectory below the DLL. Some effects may have similar dependencies, such as those that have IR files and such.
You might conceivably have an issue with some older DX plugins, but the worst case is you'll have to register them by hand using regsvr32.exe. I suppose you could also run into some weirdness with plugins that enforce draconian copy protection, like Waves. I wouldn't put it past them to require re-authorization if you move them!