Um.. answered your question exactly.

With Symlinking you have a single full install of Warcraft.
You then have copy/paste additional copies of warcraft.
Each of these copies, you delete the data and cache folders for sure, optionally the interface and screenshot folders too.
So the copies end up being very small with comparatively no space taken up on the drive.
Parent install 9 GB. Symlink copy 100mb.

You can have a SymLink with the addons and settings however you want them to be.
For example a solo wow.exe which is run with 137 addons and every warcraft setting to maximum.

Another set of SymLink folders for multiboxing with minimal graphic settings, reduced frames per second and a lot fewer addons.
These copies have smaller resolution or whatever.

Each SymLink copy of the original has the options/settings/graphics/addons etc independently set from any other copy.

When it comes time to patch, you just patch the original install, and every copy (SymLinked Folder) is up to date.