I hate to say it, but your odds are bad. In my experience, once the paint is thick enough to provide significant resistance to a stirring implement (like a toothpick), it is pretty far gone.
That said, it can't hurt to try adding a little water, or acrylic medium, and trying to stir it in with some kind of tool. If you get a lot of lumps and broken chunks of paint, it's probably toast, but, with enough elbow grease, you might be able to reconstitute it.
I'd say pick the best looking one and give it a shot. what have you got to lose?
You can look in the "Bad vallejo paints bad" thread for some advice on stirring and paint shaking tools to maximize your odds.
