Just a couple thoughts.
Independence-The kids splash pad on Independence is very similar to the ones on the Oasis class. They could be the same size. They won’t be missing out.( I have not been on Wonder, though. However if the Independence doesn’t go to Coco Cay, I’d have to think about it. Your family would be missing the Oasis lagoon pool with zero entry , a free kids water park, and the pirate ship.The chairs, umbrellas, bathrooms, and buffet would probably be more impressive to adults.
Thoughts on Wonder. You and your wife could purchase the Key. This would give you priority boarding, lunch in a designated dining room offering a modified Chops steakhouse menu, reserved show seating, two internet packages, and some other perks. There is no charge for the kids due to their ages.