Just wondering: Wouldn't symlinking the data folders cross-disk kinda defeat the purpose of having the directories separated in the first place?
You should only symlink the data dirs on the same disk.
Let's say you have 5 chars and 3 disks:
disk1: wow1
disk2: wow2, wow3 (wow2 and wow3 share data folder)
disk3: wow4, wow5 (again, those two sharing the data folder)

So, your main is using hd1, toon2 and 3 are using hd2 and toon4 and 5 are using hd3.

If you two hds, use one for the main, and the other for all the other toons.