The cars look good. The drivers are legit racing drivers. The cars are quick. They're also hilarious to watch if you haven't seen an electric racing car before. They're essentially life-size SLOT CARS with real drivers controlling them. All you really hear are the driveshafts and tires. There's no doubt this is the future, although I don't think fossil fuel racing will disappear next year or the year after.
For the organizer: A single day is a great idea for the total event. I would propose that you do things to make the event faster paced. As examples - during qualifying, show more in-car on the large screens. In between groups, have electric pace cars (like the BMW i8 or the new Chevy Bolt) out on the circuit - in other words, try to nearly always have cars on the track. Give "electric" car rides to VIPs. Create a "celebrity race" using the Bold or i3 (you could fit it in), etc. I would also propose (and you could get manufacturers to participate) an electric vehicle showroom/village. Sure, there were a few manufactures there, but you could make it even stronger.
For the fans: take your friends. Take your family. It's a single day of fun, it's affordable, and it might change your perception about the value of electric vehicles.