If you're staying for an extended stay, like 10 days..Then there's really no point in having park hoppers.
But not everyone stays that long.
I have an annual pass and my group normally goes once a month or so for about 3-4 days at a time. We normally use our park hoppers every single day we're there. I personally wouldn't like it if we didn't have a park hopper. We go to a park, ride what we want and see what we want to see..Then normally head back to the hotel for a meal or to cool off, then back out to another park. Only reason we wouldn't utilize our park hopper and plan to stay in one park all day is if we were with others who didn't have a park hopper. And as others have mentioned, it's also nice to be able to leave a park that's too crowded and head elsewhere. A few times we've been in MK and decided all the wait time were way too long and that we'd rather go elsewhere.
So to each there own and everyone does different stuff on their trips. But with 4 parks, I'd say if you're staying 4 days or less, then I'd definitely recommend a park hopper. If staying 5 or more days, then there's really no point in a hopper since you can visit all the parks at least once, then more than once depending on how extended your stay is.