A concert can be 30 minutes long and it can still be a wonderful experience if the band is amazing. I don't think the enjoyment derived from a concert is proportional to its length as people tend to get tired, hungry and cranky as time goes on. As long as the band plays well, the length of the concert doesn't really matter that much.
Generally speaking, bands give people their money's worth. The reality is that what it is worth depends on how much people pay to see them and how many people go. Now, some bands play a mere hour - that's pushing it, especially considering how expensive prices are these days. But, nothing wrong with four hours.
With the internet making music available to all, bands have to tour in order to make money. The days where a band could just sell an album and make money without having to give live performances are over. The Cure has illustrated this point. Bands today have to perform well so that other people will plunk down their money for tickets.
While bands do nationwide, or worldwide; tours in concerts, set in large stadiums, arenas, or venues containing countless seats at exorbitant prices; it almost seems like the way in which the concert industry is set-up now, prevents bands from giving fans their money's worth. While bands do put on shows, and when referring to shows, we mean the lights, the visual effects, the costume changes, etc... it seems that bands no longer give fans their money's worth, as there is no longer that intimacy that once existed between bands and their fans. Coupled with the exorbitant ticket prices, the venues in which these "concerts" are set, prevent the bands playing to even have the opportunity to properly interact with their fans; which is exactly one element of a fan getting the best experience for their money's worth. Nonetheless, the ticket holder will see a show; but it will be less a show pertaining to their band of choice, and more a show set to appease their visual senses.