It is cloaking, and if the separate pages for search engines can be seen as "differently-focused" as well as "better for search engines," then it could be interpreted as "cloaking with intent to deceive." The big problem here is that this would be a judgment call by the search engine employee(s) who reviewed the site -- Likely because of a complaint from a competitor.
Frankly, this sounds like the wrong solution because in addition to leaving your fate in the hands of a search engine employee tasked to review your site, it requires you to create and maintain a whole new set of pages. It also delivers a non-optimum on-site experience to visitors coming from search engines, and involves a confusing URL-structure.
I would recommend that you determine the actual reasons for your ranking difficulties before you do something that is risky and may make things worse. For example, re-assess the need to have such "rich" pages, and try to make search engines happier with your "real" pages before embarking on this labor-intensive and difficult-to-maintain project.
Full disclosure: I'm one of those who has little use for fancy, flashy sites with complex scripting used for page rendering; I judge sites by whether they deliver what I came for using the fewest clicks possible, and in a straightforward, simple way. Your mileage may vary... :)
I would also recommend posting this question in one of the forums where SEO is discussed here at WebmasterWorld; Your subject is far wider than the more-or-less "mechanical" subject of robots.txt function and implementation. I recommend thoroughly studying your plan and its implications before rushing to implement it in any particular way.
Also, do visit the major search engines' "Webmaster Help" sections, and read their descriptions of cloaking -- And remember *they* get to interpret what they write there, so don't read it to mean what you hope it means, read it from a "worst-case" viewpoint.