By "PR" do you mean "PageRank" (as in the component of Google's old pre-Hummingbird algorithm)? Or are you referring to rank (as in where your pages rank in the SERPs)?
If it's the former, the answer is no. PageRank is calculated based on the number of links pointing to an individual page. It's not calculated on a site-wide or domain-wide basis, so it doesn't matter how many links are pointing to other pages on "sites.google.com" domains -- the only thing that matters for PR for any individual page is the number and weight of the links pointing to that page
If it's the second, it's still no. Rankings are based on over 200 factors, of which the number of links is only one. Again, rankings are assigned to individual pages and will change depending on the searcher's query and their own personal search history, so the gross number of links pointing to other
unrelated pages that happen to reside on the same domain won't make any difference. (Especially considering this is a domain which Google is perfectly aware houses many separate websites that have nothing to do with each other and thus should not have any influence on the rest.)
As I mentioned, rankings are query-dependent (especially post-Hummingbird, with Google now trying to discern user intent instead of blindly focusing on the "keywords" they actually typed in to the search box). And they will vary depending on the user's search history. Google has been personalizing rankings for some time now. So it could be said there's actually no such thing as "a" ranking for any given page.
What's much more important to measure these days is traffic and conversions.