I would approach that problem slightly differently.
The entire bar does not need to reload.
Instead it needs to stay "current".
So to do that you load your initial value...let's say $100.00
You could even do a cool little fade out and fade in of the old vs new value.
Just have your script check every 60 seconds.
Just wait like 60 seconds and look at Google's Stock numbers - they just update on their own.
You see, on the webpage I have an electronic wallet where people click and buy things. On clicking, the database is updated but the electronic wallet, which I have in the wp_admin_bar needs to be refreshed as well in order to reflect the database changes. As far as I understand, this requires that I re-call the function get_current_user_info(); and have the text in the refresh and show the actual amount in the e-wallet.
I have looked into all the action hooks available but none serve the purpose of refreshing every 30 seconds, let's say, so I haven't been able to make a plugin or hard code the php. Does anyone have any suggestions???