Yes, they do tend to keep their value very well! OK, so my budget needs to go up or my expectations need to go down. Maybe a 2 litre M sport from 2012? The 530d was just something I fancied, I'm not bothered about speed really as I've got a motorbike for giggles and I doubt the 520d is exactly slow.
I would just go for a 10/11, it's fundamentally the same car anyway with only very minor changes. The 530d is better than the 520d, its far less like a nasty diesel.