aristotle - 1:20 am on Nov 23, 2012 (gmt 0)
^By that measure, having a bunch of pages indexed with no crawling, no titles, weird titles, and/or no description might also adversely affect the Google rankings and traffic of other pages.
If you're that worried about it, you should probably be removing the page all together and returning a 404 or 410.
Well if I understood the OP correctly, the page in question is used by existing customers, so returning a 404 or 410 would prevent them from accessing it.
As for "no titles, weird titles, and/or no description", I'm not sure what this means. Because if the page is blocked by robots.txt, Google won't have any information about the title and description other than clues provided by links from other pages, which it already has anyway.
As for the effect on Google rankings and traffic for other pages on the site, this depends on how well the content of the blocked page would "mesh" with the content of the rest of the site. On my own sites, I've blocked a few pages because their content clearly wouldn't mesh very well with the rest of the site. Several of these blocked pages on one site have even been indexed by Google because of external links, but this does no harm to anything, so it doesn't matter.