Alright I've read most of the relevant parts of ITT. I only skimmed the chapter on phrases and movements and I didn't read the chapter on performance.

I do have one question is the presence of the borrowing operation the only significant difference between Westergaardian and Schenkerian theory?

As for my thoughts, I think that Westergaardian theory is much more powerful than harmonic theory. It is capable of accounting for the presence of every single note in a composition unlike harmonic theory which seems to be stuck with a four part chorale texture plus voice leading for the melody. Moreover, Westergaardian analyses feel much more intuitive and musical to me than harmonic analyses. In other words its easier for me to hear the Westergaardian background than it is for me to hear the chord progression.

For me the most distinctive advantage of Westergaardian analyses is that it respects the fact that notes do not have to "line up" according to a certain chord structure. Notes that are sounding at the same time may be performing different functions, whereas harmonic theory dictates that notes sounding at the same time are usually "part of a chord" which is performing some harmonic function. For example its not always clear to me that a tonic chord in a piece (which harmonic theory regards as being a point of stability) is really an arrival point or a result of notes that just happen to coincide at that moment. The same is true for other chords.

A corollary of this seems to be that Harmonic analyses work fine when the notes do consistently line up according to their function, which happens all the time in pop music and possibly in Classical music although I'm not certain of this.

Having said that, my biggest worry with Westergaardian theory is that it is almost too powerful. Whereas Harmonic theory constrains you to producing notes that do sound in some sense tonal (for a very powerful example of this see here), Westergaardian theory seems to allow you to do almost anything whether it sounds musical or not. While it is very easy to come up with a Westergaardian analysis, it is very difficult for me to understand why someone who had a certain framework in mind would have performed the operations that would have led them to the music in its actual form. The main culprits of this seem to be anticipatory notes and borrowing.

One more thing: Have you read "why I am not a Schenkerian" by Lodewidjk Muns? Here is the link: http://lmuns.home.xs4all.nl/WhyIamNotaSchenkerian.pdf

One of his criticisms is that you can have harmonic consistency without following contrapuntal rules . Here is my attempt at fleshing out a more specific example: http://i.imgur.com/ruEYlhD.png I can't figure out how to generate those using using Westergaardian theory.