I currently have Scholars, and there's a good chance I'll upgrade to Gold before the year's out. I can see myself upgrading to Platinum in the next couple of years, depending on how many individual titles on pre-pub come due and what new ones come out. But, I don't know that I'll be forking over the money for Portfolio anytime soon. Several people have made comments that Platinum is really the best bang for your buck - it seems the jump from Platinum to Portfolio is just too great for many.
But, there is one feature that might persuade quite a few people to make that jump: offer unlimited free upgrades to Logos software. (i.e., when Logos 5 comes out several years from now, Portfolio users should get a free upgrade).
It'd still be a few years before I have enough money for such a package ... but that might entice me more 
