I'd say 2 is probably the least of those since winning or losing is probably not in question for most people around here after the first couple cities are built. However, there is a lot of effort put towards meeting certain self-imposed challenges: Friendly Competition in the GOTMs, La Fayette's Scenario challenges, OCC (even size 1 OCC), Early landings, High scores/HoF games, Deity+1, or just building a nice big fat civ when you already have enough to crush the AIs. With one hand, people are dissecting the game to learn more efficient strategies, while on the other hand, we put up more obstacles for ourselves to make the game more of a challenge and to test ourselves. That mostly fits with your #3 with a twist - we take pleasure in becoming more efficient and overcoming challenges previously thought unattainable.
And for the original comment...delivering to a demand city can make a huge difference in the trade bonus. I believe Uranium is a 300% bonus which helps both gold and beakers. If you can have a demanded Uranium delivery between 2 fat cities, you can get thousands of gold and beakers from one freight.