BuddyPress.org

yeh

I second to Jeff.

The best way for you will be ,create some clone of adminbar.css from bp-default,customize it to your need and then put it in one of your theme.

Now in all other themes, just use css imort rule to include this css.So you keep one place for maintaining the admin bar.

And yes,Firebug is a great addon,go for it.