Re: When does "similar" = "duplicate content" for Google?
Well, less relevance, no-index (the evil in Google) and exclusion in robots.txt is sure not the desired outcome.
Look at it from a user's standpoint. Does all that support documentation make sense if the product name is wrong and may be the version number, etc.? Either yes, then I question the wisdom of creating a new product. May be a pro version or a XYZ medical or some other add-on type product will do.
If the answer is No, the you need to rewrite the content critically. may be you can outsource it to a cheap source of writing, if you can give clear guidance what is relevant and what not. May be this is a chance to improve on the support documentation in the first place.
Another way to add information, would be to pull in relevant info on the pages, such as add a user driven tagging system, some content from an RSS feed (you news that is relevant), etc. You could also think of aggregating the content, for example instead of N pages to a particular support topic, make one page with N anchors to jump to and an index at the top. This could be done automatically if the content is well structured (like has div classes and or id's).
Just my five cents.
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