I was wondering the same thing myself. I already got all the stars I needed for Verne's daily task; what was it? Something like 1200? I'm more curious about the traffic lights; Do I use them all and then suffer until I get 5 more? Or just continue as I have been, only using 1 at the end, then replacing that eventually, (they are pretty stingy at replacing the lights) I try not to use any more than 1 or 2 and never in the same run. I don't care about buying chests, they only give stuff we all get from planes and trains anyway.
The only time I use all my lights is at the end of the event, or close to it. It usually takes about 3 runs before they have any replacement lights or any chests free or otherwise. (there is almost never any free chests)