The probloem with this low level of access requiring payment for higher features is that it's competing against things like Guild Wars and other free online play games. While the two are different overall experiences, from many sources, it seems that the base for table top RPG is shrinking. Asking people to pay to play... while possible doesn't make me think long term growth is going to be around, especially as the regular online games get mroe and more competitive and unfortunately for D&D, WoW has such a huge head start on them, especially in the fantasy field, that honestly, they will never catch up in my opinion in an online contest (as actually proven once so far with the Eberron online game.)
I don't think it's nearly as cut-and-dried that WoW is D&D's big competition as you think it is. There's an argument to be made that people who are into 'fantasy gaming' use cRPGs and MMOs as a stop-gap for when they can't get their D&D fix, not the other way around.
There
are some good video games out there, but they aren't exactly growing on trees. We seem to get one cRPG which is really worth the effort every couple of years, and a Baldur's Gate about once a decade. In between these you get the usual array of shoddy games with dull stories, frustrating gameplay, technical issues or some combination of the three. The only real exception is WoW, which seems to be perennial, but you do have to wait a couple years between expansions.
In most cases I'd rather play D&D. In fact I'd take playing D&D with a world-class DM over playing a really good cRPG in many cases. At the end of the day, WoW is still a pre-scripted game with limited player choice.
The reason WoW or a Neverwinter game win out over D&D is because you're about thirty seconds away from playing WoW at any given moment, but getting a D&D game together takes days of emailing, phone calling, coordinating schedules and rolling characters, not to mention the poor DM who is going to spend untold hours prepping for the game. Anything WotC can do to lower the threshold for jumping into a game of real D&D helps D&D be more competitive with Guild Wars, or whatever.
A robust VTT would overcome a major roadblock for people playing D&D, which is getting a group together. How many people play WoW because they live in a small town without a lot of gamers, or because they don't know anyone who plays D&D? Probably a lot, I would guess. If you give Joe Gamer in Nowheresville, KS the chance to get online and play some Dark Sun with some folks, you might actually get him to log out of WoW for a couple of hours.
I think tabletop RPGs still offer people something they can't get even in the latest and greatest video games. I don't agree that the player base is shrinking or that the interest is not there. I think lowering the threshold for getting people into a game is key to getting a D&D renaissance going.
Now if they could just fix the limited supply of really good DMs... I think WotC needs to invest in biotech and cloning. They day I can select 'Chris Perkins' from a dropdown in the VTT is the day that WoW finally dies.