I'm one of the Vanilla and BW players... moved into SC2 and slowly lost interest, mainly because of age-related changes: family, less time etc. That's not to say I don't play or don't watch, just not as much as before.
In my opinion, Blizzard are trying (albeit really hard) to do everything on their own and this cannot revive SC2. Simply because the manpower is not there. I remember Day9 on one of his talks explaining how the day9 website (THIS website) got to be simply because he joined forces with someone who was using his content - that's roughly and briefly the story, don't jump on me hardcore fans :p!
There are so many people out there who would work, a ton of hours, for free, to find and improve the game if they would be able to. BW allowed for private servers. OMG what was in there. The games, map hacks and challenges on a normal server was insaaaaane. There were also cool servers for learning and tournaments (like iCCup, battle.net for example) but many, maaaany local servers. There was a couple of hundred in my country. And each admin had his own rules, and you could do and try this and that, not to mention variety of maps. And there were a ton of people playing the game even if they haven't bought it. And that provided for a HUGE community.
There is the view that "it's bad for Blizzard business. If one likes a game, they should buy it etc." But this is, sadly, an incomplete picture. And it's not to say that whoever affords a PC that can run SC2 in a decent manner can't afford to buy the game, it's because of the kids' parents. Say a single mom works crazy hours and barely has the finances to get a computer for her kids to go to school. She's not gonna spend fifty something dollars on a game. Not when there are sooooo many other free games to play.
I think that if Blizzard allowed for private servers (which would likely mean they need to allow for local gameplay and therefore allow their game to be cracked...) the community would jump back at the opportunity to make the game their own. And it would be back :)