About the format, i like a single race of more than 60 min. Now tactics such as saving tyres, fuel and pitstop will be more important. Also concentration will become a fact to consider. If you have 2x30 min all these points won't really matter. For example: if you are a hotlapper and qualified on 1st you still have a change to finish 1st,. Try that in a 60+ min race, with steady paced, tactical racers...
I do agree with the suggestion that a grid full of experienced drivers will reduce the chance of a destruction derby. But as a experienced driver you might ask yourself: Wich is the best way to prove driver skills and insight of tacticts, 60+ min or 2x30min?