I just love the idea , but wouldn't it be great for the creepers to put tnt blocks for a sign that they are watching the player ( once the smart creepers mode is turned on ) So the player would freakishly freak out and like watch out so these smart creepers don't get to him. It would be disaster knowing that creepers are either watching you or not with you. So I think they should give a sign before attacking the player. Oh and maybe if 10 creepers team up they would become a charged creeper. Different sized creepers? I love the idea of smarter creepers. Lastly maybe the certain creepers would make you blind for a short amount of time and the other creepers would kill you. That would be awesome we could call them flash creepers.
I don't like the idea that you can't prevent the creepers spawning and just exploding, but I like the 'tactical creepers' idea, so how about a compromise.
On hard/hardcore, creepers ignore blocks when deciding to blow up.
They wouldn't blow up randomly, but instead if they get too close to you, and the only thing separating you and it was a 1 block thick wall, they'd blow up. It'd force you to make a moat or something.