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Submitting sitemaps is a good idea, especially for perticuliar bots who dont go very deep in site structure.
But I think Google dont give much attention to submitted pages.
Good rules of thumb would be to :
A link sitemap from homepage
B leave sitemap at root level of the site
The solution is presumably to ensure that all pages exist in the normal site hierarchy and can thus gain their PR in the normal manner, and aren't dependent upon the sitemap.
Another solution is to simply add a reasonable amount of text to the sitemap. However, I presume that Google are trying to remove sitemaps from their SERPs, so this isn't necessarily a useful thing to do.
Not that important, if linked from the home page. But you can keep this in mind for future sites.
While I see no solid evidence that "that Google is possibly giving a PR0 to sitemaps now", Abrexa_UK is right about trying to keep text to links ratio sensibly balanced in site maps. A good link description in text wont hurt anyone.
Google will index more pages of your site if you improve PR sitewide. Google is one of the best SE for finding pages in sites. It is picky about wich one it does include in the index. Sitemaps will help for other SE that will not crawl very deep in sites.