I figure it must be a good sign that the map editor is coming together so easily. Either I'm actually learning something about writing flexible and extensible code, or I've just spent so many hundreds (thousands?) of hours on the game at this point that all of the quirks are so deeply burned into my subconscious that I don't have problems with them anymore. Six of one, half a dozen of the other really, then.:-)
As I implied above, the editor is coming along nicely and it is currently possible to add and edit new objects (including my procedural trees), and move spawn points around, which takes care of the major features that I wanted included. Terrain editing is, for the moment at least, remaining a separate process involving the Gimp, heightmaps, and a lot of reloading of maps. It's not ideal, but it's a whole lot easier than trying to reimplement all the powerful features the Gimp offers for editing heightmaps in my own editor. One could even argue that it would be impossible.
My next steps will be to finish up a few minor features for the editor (moving trees is problematic right now, it's not possible to delete an object, and copy/paste would be nice), and then get to work on asset creation. After that I think it will be time to start beta testing because I'm pretty happy with where the game itself is right now. Don't get too excited though; that asset creation step is going to be huge and most of the assets I'm currently using will be thrown out because, frankly, they're just plain bad. However, this still marks an important milestone as once the editor is finished I will transition from programming a game engine to actually making a game. The difference may not be clear to everyone, but it makes sense to me. Honest.