We wouldn't go without them. I can't remember a single trip when we weren't in more than one park in a day. Hoppers cost more because they let you DO more. And they let you do it when you want to.Examples -
You get to MK and it's more crowded than anyone dreamed it would be. Leave and hop to another park and come back later in the afternoon when it'll probably be less crowded.
It's your "Epcot day", but you have ressies in the MK for Cinderella's Table at 5 pm (the only time you could get it). Hop on back to the MK for dinner. Then, if you want, you can grab the monorail and hop back to Epcot for Illuminations!
You're in Epcot and you want to see Fantasmic. Just grab a boat and hop over to MGM
You get to AK and find it's okay but not really an "all-day" kind of thing for you. Hop to one you like better.
You've spent the day at MGM but want to see the Spectromagic parade (it's only on certain days). Just hop back to the MK.
The combinations are endless. With hoppers, you won't have to miss anything because you can't get to another park when you want to. And, if you aren't among the lucky people who do WDW several times a year, how often are you going to have the chance to do all this?
DisFlan