I can tell that you use Delphi to write RapidPHP, so you should already be familiar with this concept. In Delphi, when you hold down the Ctrl key and click on a function or variable, it will jump to the declaration. You already have a right-click Find Declaration function, so it seems like it might be easy to bind this to Ctrl-click.
Then you need some kind of "Go back to previous edit point" command. Right now when you use Find Declaration, there is no easy way to jump back to where you were. Usually you would create a Prev/Next stack and use Alt-Leftarrow and Alt-Rightarrow to cycle between the locations. And also find the mouse Prev/Next buttons to that.
So in the best of worlds, you would Ctrl-click a declaration, then use the Back mouse button to get back. And ideally it would be able to find declarations in other files within the project (although this would require scanning files in the project tree, which can be tricky and slow).