Drink driving is completely unrelated to this discussion. The main point is that these people ACCIDENTALLY broke the vase. To me, whether they were drunk or not is totally beside the point. The only reason alchohol comes into the argument is because the OP should've realised that if you have wasted people in your home there is a higher chance something will get broken. Understanding that, and perhaps moving any valuable items out of the loungeroom, isn't treating the friends like children, it's just what anyone with half a brain would do.
four: Considering your Mum only paid $80 for the piece, how could you possibly even think about accepting more than this? In my mind you would effectively be making money off your friends and that's horrible. I appreciate its market value may be $900 but your actual loss isn't $900.
As for the 'you break it you buy it' rule that people keep bringing up, it doesn't really relate here. The OP's house isn't a shop. If you accidentally break something in a shop, the shop owner will try and make you pay, but if you accidentally break something in a bar (say a chair) the bar owner is not going to demand payment. He/she realises that owning a bar means that occasionally things will get broken. That situation is more closely related to the OP's issue that the shop scenario.
Anyway, I've been at plenty of parties where things have been broken and not once has someone been told to pay for it. This thread has made me appreciate my friends even more!