Bob has it right, just doing things bigger is not the secret to success in horror storytelling.
For horror movie sequels to work something about the story need to change. The shift from Alien to Aliens is an extreme example, where the franchise changed from horror to action horror, though I suspect that'd be a tough jump for Paranormal Activity. Perhaps if they'd turned in a more weird tales direction, or even a n out of the house "look what these ATM or other public security cameras" see point of view.
For horror movie sequels to work something about the story need to change. The shift from Alien to Aliens is an extreme example, where the franchise changed from horror to action horror, though I suspect that'd be a tough jump for Paranormal Activity. Perhaps if they'd turned in a more weird tales direction, or even a n out of the house "look what these ATM or other public security cameras" see point of view.