The Making of a Romance Trilogy–coming up with an idea

All writers have way more ideas than we'll ever write. Some ideas are merely situations and aren't enough to hang a full story on.  (With experience you can tell immediately which is which.)  Some ideas don't fit the market or that writer's chosen genre.  Other ideas can feel dated, or maybe repetitious of something the writer has written previously.  So while it's always difficult to cull through ideas and come up with the one that's right for a particular project, coming up with an idea...