^Well the Doctor did say they were assasins didn't he? Then again you could train a dog to attack people so they may be little more than animals. Yes they wanted the TARDIS but that was no different to a the aforementioned attack dogs being drawn to a bucket of raw meat. I'm not sure we know either way, very little in Blink suggested consious thought or planning on their behalf, but we don't know they're unintelligent either. If they are sentient then it's obviously a very alien intelligence that they have. Personally I hope they come back ala Blink (and given the comments about caves and bits of statues the notion of weeping angels stalking a group of people in caves does sound quite mouth watering.) The last thing I'd want to see is a Weeping Angel "queen" or the Doctor talking to the Angels.