I've been focusing this far on the visualization component, but yes there are certainly cities even smaller than SAV that have had great success with PB. Specifically, the City wants to 'gamify' the experience although I don't entirely know what that would look like when it comes to budgets.
PB could take the form of an intense outreach effort digitally with just using something like MyMadison.io or CiviComment, or it could allow for a more grown up approach in which residents each create their own ideal budget in a user interface much less complex and far-reaching but something similar to playing old-school SimCity without the whole building the city itself.
That's just the City of Savannah, though. For Chatham County and the other municipalities I haven't even been able to find a budget. I've informally requested from @saures to see if she can work with the Office of Budget and Research to get the CSVs for the last five years of the budget so that we can avoid having to spend time scraping all that data. I've done it for FY 16 and FY 17 here with a simple treemap: http://opendatasav.org/openbudgetsav