In all the years I paid the rent with software, I noticed that the best selling products were those that users asked about, and after some research I realized there was either none, or a vastly overpriced one.
I have never been able to hit the killer app that sells millions, though, just thousands. I have to admit after a huge setback in early nineties (my software company then did not survive the disappearance of boxes), it is also a happenstance that I ended up selling fonts I had mainly been creating for myself.
I guess my advice is to take any mail or phone call from customers as a chance for insight. Even the painful ones are a good occasion to elaborate strategies not to have that again.
I don’t know about features people don’t want.It seems anytime I issue a new version, someone comes around and asks for a feature I never thought about. That is usually what keeps me improving.