Dynamics make a game feel longer.
I realized this after reading an article about "Why Times Goes Faster as You Get Older." The article's point is basically that new or unique experiences act as markers in one's reflection on one's history as a whole. The older a person gets, the more routine his or her life is likely to become. By seeking out new and bold experiences, we can slow our lives down... at least in perception.
Likewise, unique and memorable experiences act as markers in a player's reflection. If you want players to feel like they have gotten their money's worth, dynamics can help create an impression of a grander adventure.