Here's my take. If the trip was planned as a way for two couples to spend time together, then if I were the OP, I'd be inclined to suck it up and go to Universal.
HOWEVER, if my DH invited friends along on our *anniversary* trip without clearing it with me and then wanted me to go to a place where I will spend the day waiting for everyone else, sorry not gonna happen. That's not compromise that's imposition. Compromise is finding a way to make everyone happy, and OP suggested a way to do so.
DH and I celebrated five years this May, but we couldn't get time away to do anything special, so I guess I'd take it personally if this was me. He special anniversary time has been hijacked.
Updated to add: I ran this scenario by my DH and he said in this case, he'd tell the friends to have a great day at Universal and use that time as some special couple time to explore the parks or have a great meal alone.
HOWEVER, if my DH invited friends along on our *anniversary* trip without clearing it with me and then wanted me to go to a place where I will spend the day waiting for everyone else, sorry not gonna happen. That's not compromise that's imposition. Compromise is finding a way to make everyone happy, and OP suggested a way to do so.
DH and I celebrated five years this May, but we couldn't get time away to do anything special, so I guess I'd take it personally if this was me. He special anniversary time has been hijacked.
Updated to add: I ran this scenario by my DH and he said in this case, he'd tell the friends to have a great day at Universal and use that time as some special couple time to explore the parks or have a great meal alone.

The theming at IOA is great and if you go you'll enjoy it. 

