GT1 and many single seaters has raced there and in future (recent rumors/plans) French GP will be held there.
Besides the lack of spectator stands and facilities, I think the track itself doesn't need much other major work. It's already Grade 1 licensed (the first requirement for F1).
F3 EuroSeries started their season there the last couple of years, as coorganising FFSA wanted to have at least one round in France. Since the Pau F3 Grand Prix went its own ways, the French round was held at LeCastellet as support races for the European Le Mans Series.
the more I look at it, the more style elements from other cars I find. Front from the FT86, rear roof line from the Peugeot RCZ, rear lights from the Audi A7, bonnet from Need For Speed Underground ...
From what I read in an engineering magazin, Drayson developed a new sandwich accumulator technique, by which every piece of the car that is made from carbon fiber can be used as a battery.