THe problem with having all of those controls, is that you spend so much time explaining to everyone how to play certain games, it can get frustrating. Even people who have played my cabinet half a dozen times still ask me the stupidest questions. Currently i have a 2 player panel with two u360s and a trackball. there are two admin buttons that light up and are labeled, exit and pause. i still get people asking me how to exit out of a game or how to pause it, and people that try to play trackball games with the joystick. i dont think i could have made this much simpler, but it is still too much to ask of most people.
as for the 4 player argument, i can see both sides. after i built my 2 player cabinet, my friend decided he wanted one, he got a 36" gateway destination monitor (800x600) for free, so decided that a 4 player panel would be best. so he has a gigantic 4 player panel with a trackball and spinner and dedicated 4way. I'd say that 90% of the time it is only used to play vertical classics, mostly centipede, millipede, dig dug, and donkey kong. but there are occasions when the others get used.
i am getting ready to put together a 4player showcase cabinet next week. even though, like my friend, i'd probably be content with only a 4way, trackball and about 3 buttons. So I'm going to move my u360s into my 4player panel and only have 4 joysticks and buttons on it. no trackball, spinner, 4way or any other stick. that way it doesnt have a cluttered frankenpanel. i will then take my 2 player cabinet, turn the monitor 90degrees and set it up with a single 4way stick, trackball, and 3 buttons. I'd be willing to bet that 90% of the time, if i am playing arcade games by myself, it will be on the classics cabinet. however i currently have two small children (3.5 years and 1.5 years, both boys) and a third one on the way in March. both of my kids ask to play on the arcade cabinet pretty frequently. my 3 year old loves TMNT and sunset riders, so i'll put him on a bar stool and we will sit there and play for a while... and my 1 year old always wants up to play when the two of use are playign these games. so a 4 player cabinet just seems like a good thing to have. i'm sure it will also be a big hit when we have family and friends over. sure that doesnt' happen that often, but a few times a year, it will be awesome. I dont too often have 4 friends over who would play TMNT or anything like that, but sometimes i will have 1 or two over, and then my kids sit there and throw a fit because they want to play too. this way i get to play with a buddy, and my kids and mash buttons and have a good time as well.