Have you ever thought of using your experience with IDEs for PL/SQL to develop an Eclipse plug-in for PL/SQL development.... I think you could charge at least as much for this plug in as you do for the entire PL/SQL Developer IDE... As far as I can tell, there is really no good PL/SQL plug-in...
Have you ever thought of providing a Subversion or CVS plug in so code can be checked out and in directly from PL/SQL Developer?
We are using subversion on my current project, and it's great!