My wife and I have been on over 20 cruises on HAL with our two daughters since 2006, when they were 7 and 8. Now, they are 20 and 21. Each time we have been in a quad. It works just fine for us - probably because we started off this way and we just got used to it. We also have some rules to preserve the peace. For example, for "number 2," we use a public rest room. We also split the beds to gain more room.
We've had some new challenges as the girls have grown up. One is 5'10" and the other is 5'11". So, it is now my wife who gets the couch! And, yes, my wife and I also eagerly look forward to our cruises by ourselves.
On most cruises, the girls have been free - we just pay their taxes and port fees. So, the economics make this fairly compelling. We prefer to spend the extra money on our private excursions. Yes, it may get cramped, but it's one of the few times that we really get to hang out together. We watch movies as a family, and we play Uno and hearts. I have a still busy legal practice, and they are now in college. So, these are truly precious times for us being able to hang out together.
Sure, there are sacrifices, and, yes, tempers sometimes flare up. At the same time, we can all recall famous stories about the really stinky fart, or how we had to take four showers in 30 minutes to make dinner. These are the things for which memories are made!
So, I wouldn't so easily dismiss the quad. It really just depends on your family, your habits and your expectations.