Digital Producer has reviewed a feature that a competitor (Adobe Audition) calls 'Automation Lanes' which is simply a separate track for different types of envelope points to reduce confusion and clutter. Seems like a fine idea.

http://www.digitalproducer.com/articles/viewarticle.jsp?id=68132

Guess a Vegas work-around could be to open the same audio file in adjacent tracks and apply a separate envelope to each, but that sounds awfully processor-heavy.