I haven't posted or been on here in months, so I don't care if I get banned at this point; therefore, I'm just gonna go ahead and be straight up
What you're really asking here is, "If I give up on realism and half-ass it, will people still be willing to pay me money?" The answer, generally, is no. Not unless they really like your music specifically.
For every good indie game with a retro soundtrack, there are a lot more that use the "retro" shtick as an excuse for having shit visual fidelity and dated gameplay and hope that equally dated music will be cost effective and people will give it a pass because "it's retro". Most worthwhile modern chiptunes actually have pretty slick production values with a pseudo lo-fi sound.
What most people don't realize, is that the old soundtracks were as memorable and effective as they were because the composer had to know his/her stuff. Due to a severely limited number of voices on the soundchips of yore, composers relied on (masterfully written) polyphonic scores to create flowing music; they had a solid grasp on melody. It's not like now, where you can buy an M-Audio Keyboard, an expensive sample library and hold down some block chords, pound some drums and string ostinatos like everyone's favourite film composer who dumbed Hollywood Orchestras down to a pop band playing through string and horn ensembles — fuck the woodwinds.
My point is, there is a market for retro scores, but it's more in being able to write in that style with a limited number of voices than in a dated sound. If you're aiming to make money by specializing in retro scores, just be sure you're music is closer to Yoko Shimomura than Hans Zimmer and don't expect lo-fi to give you a pass.