Have done both, although maybe 20 years ago. Tough choice. Agree with Bob806 that Sleeping Bear has some major dunes and natural areas. But Cedar Point has the most amazing roller coaster collection, probably in the United States, but definitely better than any in my area. Coasters at Cedar Point were two to three times the length of any at Kings Dominion, the best alternative in VA.
Look again at the schedule. Neither area seems to require 5 days in my opinion. Why not 3 days of quiet and family time at the Dunes and then two days for Cedar Point area. When the children are young, a good approach is to attempt to have a variety of experiences for them to remember and someday replicate for their own family. Really tough to avoid a tight schedule when you only have a week or two of vacation.
My wife and I are retired now and we have been revisiting some locations to see things in more depth. Too bad our careers don't offer the choice of doing things at leisure when the children are young.
