We also have never gone more than 4 nights because we're young, walk fast, and can pack a LOT in in that time and a trip to WDW is crazy expensive. That being said, that pace can be exhausting and for future trips I am definitely going for longer to enjoy more pool/leisure time/doing some things outside of the parks that I always wanted but never got to because I didn't want to waste the value of my park ticket.
Regardless of length of stay I consider Park Hoppers a must and well worth the extra $. I prefer having the option to do whatever park fits my mood at the moment, and the ability to visit favorite parks/attractions multiple times without being locked in to a specific day.