I think it should really be based on a game by game basis, just because its next gen doesn't mean it should cost more... Demon Souls aklthough pretty, has fairly basic animations and is clearly not the most ambitious undertaking compared to the average AAA game.
Personally I wouldn't pay extra for any of the launch titles, games like GOW2/Horizon? Sure.
It is based on a game by game basis and Sony says as much. Their own games will cost between $50-70, so not everything will be $70. It was the same for Sony on the PS4, only that there the price range was $40-60.