I like scenarios for a plethra of reasons. Not only to re-play history, but to learn a bit about history. As long as the scenario is written well, I have learned a lot about history from different scenarios. In the Civ2 Red Front scenario I really learned what scorched earth policy meant.
Also, my wife's favorite Civ 2 scenario is the genetics one where you get to direct evolution. She learned enough to where she wanted to learn more and now works in the health-care profession.
Also, they are fun as they add a little demension of fun if/when you get bored with the regular game (ie beating it on Diety with all civs and no there is not much more of a challenge.)