i encourage you to keep improving this.
software should never be "final"
if all you ever wanted to do was make a RGM+ then you already did it, just finish the manual and bugfix. i just don't think that should be the end.
if a new rendering engine can allow you to implement new features into the editor, then i say go for it. take your time. if you work on this project for the next 10 years, improving it and expanding it, then people will keep buying it.
i know it's not your fulltime job. noone can realistically demand you "fix this asap" etc etc.
if it was libre-sourced other people could help you. but i know you don't want to do that.