My love for Coda knows no bounds. Except maybe the bounds of the tab bar.
One especially sprawling project at work brought the problem to a head: switching between all the files had simply become too tedious. Rather than desert Coda (perish the thought) I decided to whip up a plug-in called Wing Man. Panic has a pretty good how to on the basics of plug-in building so I won't rehash all of that here.
A few points of interest to others interested in creating a Coda plugin:
You'll need to grab a copy of CodaPlugInsController.h from one of the sample projects.
Be sure to compile the plug-in bundle as 32-bit Universal.
To set the architecture of your plug-in bundle, right click on the bundle in the Targets section and choose Get Info. Choose 32-bit Universal from the list of architectures in the Build tab.
The bundle extension should be codaplugin, not bundle.
To set the extension of your plug-in bundle, right click on the bundle in the Targets section and choose Get Info. Set the Wrapper Extension to "codaplugin" (without the quotes) in the Build tab.
Wing Man on github