In my mind, that's where appealing on multiple fronts comes to bear. I've seen games with essentially a dead board on gameFAQ's serving as the closest thing to a proper discussion of it UNTIL somebody/various people started concocting Let's Plays on youtube for them. Suddenly, people have things to discuss about the game based on the video, people that totally missed out on the the first time around are asking what it is and where to get it, and all is for the better on it. There is a fair chance that no matter what is done, some players will simply enjoy the game and not mess with any discussions, which is fine, but I can't shake the feeling that there are a good many people that wouldn't fall into that category considering the tremendous amount of players that wind up actively discussing various games in other genres.
As to audience, again the Mystery Dungeon series of graphical Roguelikes tends to sell many thousands worldwide, some in the million+ range. From a broader point, the Diablo styled games are also pretty key sellers with many Roguelike elements at their core...so there are surely potential fans in there. As a given, there's POWDER, ADOM, Nethack, and Crawl folk and the mysterious smattering of PC roguelike players in general. Roguelikes have tended to be more esoteric in terms of presence and such versus racing games, platformers, etc---which has worked to an extent, but I reckon now is as good a time as ever to get some spotlights going.
Of course, the other trick to grow an audience is with games that reach around to other genres---Spelunky being an excellent recent example.
For a random example relative to Karzack's: Roguetemple could join in/contribute to clamour for the upcoming hopeful release of the big Incursion rewrite currently due out at the end of October as they've just a google group and a megathread on Bay12 and Something Awful to my recollection.
Edit: Scrub that last bit as more of a long term eventuality...looks like the Incusion page was update a little while back leaning things moreso towards an October 31st 2010 release versus this year---though he is about half done with the sprawling changes and improvements.
