If you have a 1 run game in the 9th versus a 1 run game in the 7th, then certainly, everything is more amped up in the 9th inning. But if you have a 1 run game in the 7th with the heart of the order coming up versus a 3 run game in the 9th with the bottom of the order coming up (or worse, the game could be lost by that point), then I would have to disagree about the 9th inning being more amped up.
The problem is, when you have a high leverage situation in the 7th, you don't know that the high leverage situation will still exist in the 9th. IMO, it's better to save the game when the game is on the line, then worry about the 9th inning when you get there. I'd prefer not lose the game with my best reliever sitting on the bench.