Don't give up!, but in answer to your question. I'd be pestering the police everyday to find out what is happening in their investigation. You must have a crime number and contact, so be a pain in the arse!
You've lost a lot of money, are a victim of a crime and have a right to know what's going on!
You have the address where you bought the car from so you can find out who owns the property which is a start and the name of the fella that took your cash although that's probably false. Get on the net, it's amazing what you can find out. Google, facebook, Land Registry, The Phonebook, 192.com, Electoral Roll it's all out there, and yes if needs be go back there knock on a few doors talk to the neighbours! What sort of neighbourhood was it nice? rough? If it's a rough area I doubt anyone will want to know, but if it's nice then people might be quite talkative!
To be honest I doubt the police have done very much, especially if they think you're not bothered....
The other thing I'd do is forget the Beemer and buy a nice cheap car for the time being as Al suggests! How about an Omega?