I have had good reults by using a 301 from one old, unimportant page with good SERP to a newer page. I have a number of old, unimportant pages and I am wondering if it would be a good strategy to redirect them all or a number of them.

Example:
old-what-are-widgets.html
old-blue-widget.html
old-red-widget.html

Redirect to:
what-are-widgets.html
blue-widget.html
red-widget.html

or

important-widget-page.html
The single page is much more important than the group of pages. Would I be wasting value by having them point to the single page?

send them to the most appropriate pages... your rank will increase across the board and pass around... giving site lift and the individual pages for keywords

In general I do redirect one page to one page but I do have a case where there are 8 pages (6 have PR4) that are obsolete, provide no value to us and could appropriately be redirected to one page. I am just wondering if that SERP and PR value would be lost or would be aggregated.

Redirect, hoping to retain SERP and PR? It would massively defy all logic for your not to lose those. Replace the content on the redir page with the target URL's content (a copy, with enhanced text)...

As long as the search relevancy for the old page's SERP listings still apply to the newly 301'd page, you'll be fine. But if a page was ranked for terms that don't apply to the new page it's redirecting to, it's only a matter of time before the ranking gets readjusted to the new page.