Re: Dashboard ?
1. the only way to get to the buddypress.org WPMU dashboard is by typing the url into your browser, or clicking the link you posted above. that page is only their for andy to update this site and his blog (https://buddypress.org/blog).
On your own site, if you would like them to use that dashboard, you could post a link in your navigation bar?
2. yes, technicaly speaking, every user on this site has 2 dashboards. however, the wpMU dashboard has no user-features.
On your own site, if you enable user-blogs the WPMU dashboard would allow them to post to their blogs, ect. as andy has them turned off on this site, the WPMU dashboard is simply their for peaple to admire its good looks 
3. it depends on if you have user-blogs allowed. on this site everyone (other than the admins) sees the exact same thing.
In a future version could you add a new admin-setting so that the admin section could be turned off to users? when its turned off they get redirected back to buddypress?
