I've got a page I created under Home using a page type that has "Exclude from Nav" UN-checked.
In the Dashboard site map, it appears right underneath the home page. In the nav blocks on any of the top-level pages (including home), it does not appear, but all the rest of the pages under the home page do.
On a page with a site map block, the page does not appear.
I'm probably overlooking something obvious, but what? I cannot seem to find any other page properties that affect how it is displayed in the navigation system.
Also make sure you didn't futz with the auto-nav settings if you have a bunch of pages directly under home instead of in a tiered structure.