There's a common misunderstanding here - a page doesn't lose PR by linking to another page. Yes, your page's PR is used to "weight" your vote for the page you link to. But the linking page's PR is not demoted or diminished by voting for other pages. There's nowhere in the algorithm that deducts a little bit of PR for every link that's on a page.
If you think of the idea of a "random walk" of the web, then PR is a measure of how likely it is that any given page will be found in a random walk. You can see that linking out from a page does not make it any less likely that page will be found by a random surfer. The effect of linking gets measured AFTER the page is already found.
I think the misunderstanding comes because the total weight of a page's vote is chopped up among all the outgoing links. So, a links page is passing less PR to all the other pages with every link it adds - and that includes the navigation links that stay within the site. So, a links page is usually less help to the rest of your site than other pages are. It definitely still helps your other pages, but that help is diminshed.
If you use a noindex, nofollow - then your links page is passing on no PR at all -- not even to your own pages. You just shot yourself in the foot (well, the toe) by trying to hoard PR.
I'll say it again - "passing PR" does not downgrade the linking page's PR one iota.