1) the benefit to putting the pages into there own folder is a extra layer of protection, perhaps a small layer, but still an extra layer.
a malicious hacker that can easily find your admin pages may try to use brute force hacking methods to gain access. if the admin pages cannot be easily found. Why easily give away the location of the admin pages?
2) personally, i prefer not to include the admin navigation on regular pages. Again, if malicious hacker uses brute force techniques to gain access to your site, you are giving him a road map to the admin pages.
