I'd say it is worth it -- but I hate to see you have to blaze through so quickly. You can see portions of all of these parks from the roadway overlooks, but to really experience the grandeur, you have to get out, walk around, sit a spell and soak it up. Sounds like you'll have a little time for that at South Rim, but with only 3-4 hours at the other three, there won't be much opportunity for relaxing.

But, on the other hand, I've more often done it the way you are suggesting and I would not trade those experiences. So I say do it! At the least, you'll whet your appetite for a return visit another time! Bob