It's worth noting that by August next year, the East London Line will be working.
This means much higher profile train services to Forest Hill, much better Sunday services, and more capacity generally.
There would be some merit in publicity for next year's event emphasising this new development. Though however much one bangs on about public transport, some will still use cars.
E London line could encourage Horniman to run more events, which, if they are manageable, could be a good thing. However, over-excitement about the potential of the line could also lead to more activity than the local community had bargained for.
I think this in one for the Forest Hill Society and Tewkesbury Lodge Association to raise both with the Council and the Museum Trustees.
It would also incidentally be worthwhile to look at a series of suitable activities to help celebrate the new service.