My husband insists on hopper. I think we could make it without it except for AK and MGM. We never spend a whole day at either one of those.
Personally, I don't find any of the individual parks worth their admission, but the hopper adds the value to it. Plus, while it is definitely worthwhile to go on your favorite rides more than once, it's much easier to be spontaneous with the hopper. I just don't understand how people can plan their days so precisely. I like to do things as the mood arises...without a hopper I couldn't!