Everett,

Thank you so very much for the thoughtful and really helpful answer.  We will implement the robots.txt disallow statements you suggested, and I will discuss with my developer the ability to reference just the id portion of the url.  We've begun the URL removal process in Webmaster Tools, and fortunately, in the vast majority of cases, the content hasn't been indexed due to robots.txt--just the URL.

As far as all of the hrefs diluting pagerank, what are your thoughts on nofollowing these links?  We've had this on the table for some time, but haven't been able to come to a decision. It would curb the pagerank dilution, and it would probably keep Google from indexing those robots-disallowed pages. It's good to know these pages probably wouldn't ever trip a Panda/dupe content filter, but it still seems cleaner/neater for them not to be indexed at all. That said, I'm afraid nofollowing the links could look suspicious to Google. All combined, it would result in 25-35 nofollowed internal links on each page, with about the same amount dofollowed (if you include navigation, etc).

Thank you again for lending your time and expertise to this answer.  It is truly, truly, truly appreciated.