My search for a new editor still continues. I've evaluated Emacs, but I can't feel comfortable with it: the key bindings are alien enough compared to all the other apps I use with GNOME that I kept doing things like accidentally cutting (control-X) or printing (control-P) things with GNOME apps, and searching (control-S) instead of saving in Emacs. After about a month of active Emacs use, my fingers still hadn't gotten used to switching contexts all the time.
I've also had a new look at vim, and it's also not something my fingers are going to be comfortable with in the long run. Kate, from KDE, feels alien as well.
Gedit would be fine, except it wants to run only one instance. If I run it a second time, it detects the first instance, and opens a new tab or new window using that instance, and then exits the second instance. This makes it wholly unsuitable to be used as $EDITOR. Also, it doesn't seem very intelligent in its handling of TAB characters: I can (and I want to) have it insert spaces when I press the TAB key, since that causes the least amount of trouble when formatting Python code that gets exchanged with other people, but I still want to write Makefiles. Gedit doesn't seem to let me do that.
My two best options seem to be to hack Gedit to fix the problems I have with it, and to write a new editor of my own. Given how easy it is to write quick-and-dirty apps in PyGTK, they're probably both about the amount of work, at least initially.
My NIHolic tendencies would indicate that writing my own editor would be the logical choice. The rational neuron in my brain insists that fixing Gedit would be the better choice.