I upgraded my pass for the same reason - I have out-of-state family visiting for a week in November and we had already planned on buying memory maker. It was cheaper for my family to have one person upgrade now than to pay for MM. I went from a FL resident pass with water parks (don't remember the name of that pass) to the Platinum Plus pass for about $75. The rest of my family are waiting to upgrade when they have to renew next October.
Sounds like you are saying you were able to upgrade just one of your family members passes ? When I asked in the parks last week the guy seemed little confused and said you have to do all of them which didn't make sense.
But it sounds like you might have had success doing one only. Should have tried a difference CM. We have three more trips planned so it would be worth it. I will try when we get there for the next trip.