I view them as highly popular. Popular enough that somebody made NDS homebrew to play them that has now been ported to more systems than I can count to the point that new games converted to the format aren't even compatible with the original player. Some really popular and high quality shows have been based on them (Clannad, Air, Kanon, F/SN, Steins;Gate, Robotics;Notes, etc.) and each of those brings new fans to the genre as well, alongside that, fans of the genre are usually very avid. I find more fanfics for visual novels than with most other things of similar popularity in media, entirely because of their interactivity, so if you're worried about the popularity of visual novels, fear not, the market is massive. If you're looking for recommendations of some to read for inspiration or just because you're interested, shoot me pm.