On expanding the audience, I noticed with approval that my FLGS carries "The Idiot's Guide to D&D". It does a decent job of explaining what's going on for complete newbies. It's possible that with it, and the PHB and DMG and a module, someone could teach themselves to play without the usual helpers.
I think that might expand the game, mostly because it could lower the intimidation factor for new players. This particular FLGS mostly sells non-RPG stuff -- Warhammer, board games, puzzles, etc., and their audience is a mix of 8-40 year olds, with the younguns sometimes crying for D&D, with apparently knowing what it is.