For. It's the 'unlimited' opportunity of the Premium account that makes it worth it for me.
Having a clean, easy-to-navigate portfolio and website, both allowing unlimited uploads, is worth it.
The ability for visitors to view those unlimited images, in a variety of frames and mats is worth it.
Even if I never sold anything here, I'd stay for those two reasons. Plus, any additional place to potentially be noticed, as Mark mentioned, is a positive thing. The possibility of sales being transacted while you sleep or go about your day, is gravy. ;-)