Re: Deleting a certain part of the navigation
We had a similar issue and chose a soft solution with CSS so we do not have to worry when upgrading.
We placed this in the site-wide.css:
#wp-admin-bar #bp-admin-blogs, #bp-adminbar-blogs-menu {
display:none !important;
}
#my-blogs {
display:none !important;
}
So the functions technically remain but are just not displayed. Works for us.