I absolutely agree with GSS that understanding inversions are important. They may be even more important to understand on a guitar where the sound can be strikingly different between voicings. But my point was that the guitar fretboard, being non-linear (or multi-linear?), makes it harder to illustrate the fundamentals of intervals and scales to the rank beginner. Peace.
Oh, and I would say that for teaching the sound of a particular interval and especially for illustrating the portability, or relativity, or whatever you want to call it, of chords and intervals, a guitar is excellent.
-G