and how many regulars/good contributors wouldn´t be here if phun was private?
i´m sure some database-care and archiving of old threads as bama mentioned will certainly help. there are also many "suggestions" for server-/mysql-/... optimizing availabe in relevant vbulletin-support-forums. someone with access and experience just needs to take a look... probably one of the tech-guys of our hoster?
phun causes a lot of traffic, but there are many sites around with not significantly less traffic, but lower hardware-equipment that still run smooth all day.