A lot of you made excellent points. The 2 responses that I adhere to the most are Glitchfinder's & Kain Nobel's. The amount of revenue that you're hoping to obtain from an RTP-based game depends on your target market, the presentation of your project, and the overall quality of the game.
Target Market: As mentioned previously, you'll ideally have much more success trying to sell an RM game to the general public, rather than communities that are based off of using that particular game engine. RM users have become accustomed to the default style so your main character, for example, is being related to a game that person just played last week.
Presentation: Even if you produce a top-notch game, if you don't prove to people that it's worth the money, then there's no motive behind taking that chance. This can be achieve by going above & beyond by releasing a demo, capturing in-game footage, making a fancy manual, making a clean & detailed thread, etc.
Overall Quality: This basically reflects the amount of effort that you put into the game. If you don't touch any of the RTP, whatsoever, and decide to use them as is, then there is no way I will be buying that game. AT LEAST frankensprite, recolor, make edits, include custom images, etc. Other factors that are obviously important include designing unique mechanics, original items, creative elements, status ailments, and much more.
So all in all......I would purchase an RM game on a rare occasion.