Do you have somewhere better to be than at the golf course? If so, why not just go there and not to the course?
I'll try to answer your 3 questions Jason.
1) During MOST rounds on MOST courses 4 hours is sufficient to play an enjoyable round of golf and 5 is unnecessary. MOST 5 hour rounds involve a lot of waiting and standing around either for the group ahead or a slow player in your group. The waiting which as some have pointed out takes away from the rhythm of the game and takes your mind more and more off your next shot and the round itself. During more competitive rounds however much of the extra time is spent making extra considerations for the next shot especially lining up and reading putts on the green. In cases of 5 hour competitive rounds the extra time is not AS bad (meaning I'd still prefer quicker) as a casual round with friends (game or not)
I will say a 5 hour round also doesn't bother me as much when I am riding a cart because I usually am already distracted by other things like where to drive the cart to next, how many beers are left and tweeting that I won the last hole on Jones.
However when walking during a casual round on MOST courses 4 hours is plenty of time to play in and at a nice pace in rhythm with yout game. The extra hour could be used better elsewhere in my life and that is what is wrong with a 5 hour round in my opinion.
2) Than on the course for that extra hour or so? Yes I'd rather be in the clubhouse sitting down enjoying a cold one while reminiscing about the round I just played in 4 hours or less.
3) 5 hour rounds or doing something else with my life aren't the only two options. If you are trying to make us pick between only 5 hour golf rounds and other things in our life I would suspect that golf would lose more play.