It's already been confirmed that a majority of the expansion pack's assets will be downloaded to clients regardless of their expansion purchase, by necessity, to allow non-expansion players to play alongside players using the new race/jobs/gear. Even with most of that data copied from physical media, there will still be some form of patch download. You're getting the expansion data whether you want it or not.

I still have access to my Legacy account privileges and CE content from PC, even though my PS3 copy is the "Standard" edition off of PSN. All you are really getting with the expansion pack purchase is the "right" to access content patched in at 3.0, so I can't imagine it being something you'd need to buy twice. It seems like it would be more work for them to try and enforce two (or three) different levels of activation on a single account.