I am not a subscriber but am a current customer.
About the current incentives for subscribing:
I haven't had a chance to try the Premium Browser, but I doubt I would want to use a separate program just for one site. Is the Premium Browser MSIE based? I wouldn't want to use it for that reason, also, if that is the case. (I am not trying to start a browser quility discussion, it is just that I don't use MSIE unless I have to and am very fluent with Firefox, so that's what I'd want to use even as a subscriber.)
The premium suites also are not strong draws, again this is just my personal opinion. I have never bought one, but are they based on the same Theme Manager as the recent Skin Factory / Alienware suites? If so I would be deterred from trying them, as I found it conflicted somewhat with my other StarDock programs, especially on uninstallation. Plus, much of the enjoyment of customization is piecing together one's own suite from what you like--there are a lot of top-quality windowblinds and icon packages to play with for free.
Personal pages and photo albums are neat, but, once again not something I would want to spend money to have. In my experience viewing an artists skins or articles is all I need when I want to follow a name. And other than being associated with WinCustomize, the personal pages have little to offer than one could not get for free elsewhere.
As a current customer I have unlimited bandwidth already, and generally the files used for skins are so small that a faster server would not make a huge difference to me.
A benefit of subscription you do not mention is the ability to rate skins. In this case I do wish I had that.
I love WinCustomize and Stardock software. Use them both all the time. Great stuff. So great, in fact, that the free or customer access has so far been very sufficient for even my own avid needs.
So, now that I've said why I haven't subscribed, what would change my mind? A more thorough search feature, for the forums in particular, would be appealing (although hard to justify providing this to only subscribers). What about things like larger avatars, signatures with or without images, or interesting "titles"? Would you consider bundling some software (other than Premium Browser)? Say an extension of ODNT subscription, or a copy of ObjectDock Plus, or a game even.
Again, WinCustomize and StarDock offer such great services and products at the free and customer level, there is little I can think of to add to that which would justify an additional expenditure. I hope this doesn't encourage consideration of scaling back those features for the unsubscibed, though!