It shocks me that a millionaire who has already saved up enough in a tax-advantaged account stresses about these decisions. No one should tell you what to do with your money. But for you, the question is no more consequential to your long-term financial well-being than asking, "Why buy a Rolls Royce when a Honda will do just fine?
Many of the parents I talk to about my alma mater ask questions like how much debt are they expected to take on and whether education loans require credit checks. They are almost always surprised when I tell them that no loans are expected. Some of the students deal with issues like how to pay for books and personal items when they send their work-study earnings home to help meet their families’ needs. They are always reluctant to reach out for extra financial aid. And despite the fact that most students get financial aid, those from families earning the median income of $60-$70k/year or less often feel desperately isolated and left out because of tight finances.
I don’t mean to be callous, but compared to their concerns, yours just seem less urgent to me. Tell your child to go to UMass, it is a great school in a wonderful town, and keep the 529 for your future non-existent grandchild. You’re probably right that it won’t make much difference in your child’s life. But, I really hope my alma mater does not spend a second worrying about ROI for you.