Soldato
I know you were trying to make a point, but it's 37,000 in the grandstands and the BBC reports closer to 200,000 in total attendance from the balconies and hillsides*. Its status does justify it on the calendar, despite it not always being the most exhilarating race to watch.
*http://www.bbc.co.uk/sport/formula1/22654574
It has been trading on its status for over two decades. Never mind not being exhilarating, it isn't a race at all. If it wasn't on the calendar now, it wouldn't be considered as a new race today.