Shame to say it but this type of thing is not "unbelievable" or "surprising" and probably happens all the time all over the country, I'm very lucky now to live in a quiet village where this type of thing just doesn't happen but it is a true reflection on modern society and I have been the victim of the exact thing a long time ago when I had my S2 RS Turbo.
There are far too many people out there who want everything for nothing (and quite often get it) and can't stand seeing others with nice stuff who've worked for it. Basically they've thought there's a nice car, he's a w*anker lets wreck it. It's more likely that if they were caught some social worker would say it's not their fault, they're the ones needing help.
Simple fact is that until this country gets tough on all forms of crime again things like war memorials being looted for scrap, grannies being robbed and mindless damage to people's property will continue and probably increase.
This will no doubt have an impact on you for weeks if not months and I bet the little scrote that did it has already forgotten about it.