So, after struggling with horrible interface choices of Xcode 4, I'm finally on 5.1.1.
The tabs became almost usable. Double clicking can be configured to open a file in a new tab. Good. Double clicking another file opens it in a new tab. Good. Double clicking first file again switches to previously open tab. Good! Double clicking first file while it is open in current tab opens a second tab with that file. Ok, I can live with that, since from there on they just switch from one to another.
So far a surprisingly sane behavior.
Unless you make a single click in the navigation panel by mistake. Single click opens whatever you click in the current tab, all logic and reason be damned.
The question is, how to change single click behavior to "Use separate tab" (or however Xcode refers to that behavior)?
Is there any way to disable single clicks from doing anything at all aside from highlighting the selection?
There's no option to disable the single-click behavior. Two options that get you close to your desired behavior are:
Use a single separate window for most of your tabs. Use a "main" window that has the file navigator visible, and a separate "work" window with the file navigator hidden. If you want to add a tab to the work window, create it in the main window and then drag it's tab over to the work window. This is an extra step, but you'll never have a single click change any of the tabs that you care about (thought it'll still change the primary or focussed editor in the main window, depending on your settings).
Use separate windows for each file. There's a preference setting that lets you create windows instead of tabs when you double-click a file in the file navigator. Use Mission Control instead of the tab bar to navigate between your files.