OP here. So the weekend in question just wrapped up. I did indeed go on the trip, and I am glad I did.
The discomfort of being at the "Ark Encounter" lasted about 4 hours (the amount of time we spent there). If I held it in my mind as a Disney-like exhibit it was bearable. Interesting, even, as a fictitious imagining. Mom was super happy and didn't actively try to proselytize us - or at least no more than usual. My sisters and I exchanged looks periodically at some of the creative license that was taken in the exhibit.
Both mom and dad used wheelchairs at the ark encounter, a first for both of them. They don't use chairs normally but there was a lot of walking involved and they would not have had the stamina to be on their feet the whole time. That was sobering.
The best part of the weekend was being together with my sisters and my parents - something we haven't done in decades. We went out to a nice dinner at a Capital Grille one night, to celebrate mom's birthday. We spent the other evening playing cards and doing an old "night of beauty" ritual which we co-opted our dad into joining. Lots of laughing and joking, which is the comfort zone in our family.
So the trip was a net positive, and a stark reminder to me of my parents' declining health and how few opportunities like this I'll have with them.
I am now researching orgs to donate 3x to. :)