
Well, WebSite Auditor aims to cover the whole onpage optimization area, that is why it now has the second, larger module that addresses other factors (broken links, HTML validity, indexation, duplicate content etc. etc.) in addition to the older page analysis module. SEO PowerSuite consists of four modules that are to cover all areas of SEO and WebSite Auditor is just one of them.
I would not agree that it is a "waste of time" just because no one part of something whole can be useless by itself. Onpage optimization alone can be a winning strategy for some low-competition keywords, there have been examples of that. Moreover other SEO activities, such as link building, will be much more effective if a site has been initially properly optimized.
Of course there is no sense in getting stuck with the idea of dominating the % score by several percent, what you need to focus is the readability and appeal of your text AND at the same time sufficient (that is, practically working for the top 10) keyword density.

Thanks for your reply. Does WA still make its on-page recommendations and scores based on the on-page factors of the top Google competition? Or are the scores and recommendations now taking into account both the on-page AND off-page factors of the top competition sites?