3. Security:
Pakistan's nuclear weapons have in fact played a very large role in its security, in preventing wars imposed by India, as well as preventing the US from pushing into Pakistan and destabilizing it. Were it not for nuclear weapons, why would the US treat Pakistan any differently from Iraq, Afghanistan or Yemen. While the US would not likely invade Pakistan after the fiasco in Iraq, they certainly would not think twice of launching air strikes where they pleased, or being too concerned about Pakistan's stability.
So in terms of Pakistan's security, the payoff from the nuclear program has been huge.