Viky, having proof is better than having none at all. You'd have more chance of the police acting upon it - especially if the culprit is a known offender. What is the alternative? Sit back and do nothing and let these mindless vandals make a misery of your lives?
As a matter of interest, up until about three years ago we had a similar problem in our street, with a particular gang of kids who got some sort of kick out of smashing wing mirrors off cars. A lot of the neighbours got fed up with it and installed CCTV cameras (some have chosen large cameras because they want the vandals to be aware that their cars are being monitored) and I can honestly say this has acted as a deterrent... Well, put it one way, we've had no problems in three years. I'm sorry that you don't feel that this would work for you.