Yes I like that idea too. It may help raise more money for museums and other heritage organisations as well.
I think certain enthusiasts may not like non-enthusiasts getting on though - some of the attitudes from some on running days towards people is not really great. For example, being aggressive with people getting in the way of photos or getting annoyed because someone called an RT a Routemaster. I was once called a four-letter expletive just because I accidentally walked in front of someone taking a photo!
Anyway, my grievance aside, I think it’s a good idea. When there used to be the Herne Bay Bus Rally, it was popular with local tourists often with young families who wanted an open top ride along the seafront. I’d even suggest enthusiasts were outnumbered at this event, which usually took place in the height of the summer during the Herne Bay Festival. So, I’d say the market is there if advertised properly.