WRT disabled() - that makes sense.  Looking through core, however, there's actually no instance anywhere of disabled() (or the other helper functions) being run through sprintf() or printf().  There is, however (especially with checked()), precedence for putting it directly next to the attribute.

So with that in mind, what I'd actually suggest is removing the placeholder for disabled() and putting that directly in the variable - next to wherever you want it, sans extra space.  I think that keeps up with your note of maintainability/readability.  And it eliminates the extra space.

That work for you?