When you try to target too many keywords (or keyphrases) on one page, it dilutes the keyword density for each of those keywords.
You'll get higher search engine rankings and more targeted traffic if you limit your keywords to two or three per page. Any more than that and your search engine rankings will be poor for each one.
Twenty pages, each targeting two keywords, will bring in more traffic than one page targeting forty keywords, and that traffic will be much better targeted to boot.
Those twenty pages, each focusing on two keywords, will provide twenty "roads" from the search engines to your website. This gives you a much greater chance of being found in the search results.