You probably need to split the group.
Is it worth it? Yes. theming and two major rides fantastic. It's a must if you're a HP fan. I'ts a must if you want to see something which, IMHO, exceeds Disney. It's a must if you don't know when/if you'll be getting back to Orlando.
It it worth it? NO If this is your first trip to Disney. If you haven't to Disney much. In other words if there is a still stuff on your "must see" list. It's not worth it if you're on a tight budget. The extra $100 pp could pay for a meal at virtually any restaurant at WDW.
Anyone who thinks they may go back to Universal in the next year should consider one of the annual passes.
I cannot speak for the other girls; some have done WDW a number of times, others it is their first time. But there is a lot of "well, if my friends are going to Universal, I want to..."--that is definitely what I am hearing from my DD.
I would rather spend $25 for the extra day at WDW BUT I do have an interest in Universal & I like big rides even if she doesn't. And if we can buy a 1 park pass & hit Adventure Island--appears to be the bulk of the HP items, which is their focus.
There was overall balking at $150pp. But around $100 for one park seemed more palatable overall.
When we began planning this trip several senior mothers didn't want to do it again...oh, I have to walk so far to get coffee at the resort...I couldn't buy a cup, I had to buy a refillable mug to get coffee (not true...)...food sucks & is expensive at WDW, etc. etc. I said, hey, we have been 2x, and I did EXTENSIVE research so I can tell you where the food is pretty good & where you can get a better deal, which rides are best, etc. etc. There always have to be some whiners...
We did WDW for a week for each of our previous trips, with nothing else on our agenda. This is 3 days, really half days at best with the competition activities. That's why I wanted that whole day, but I'm game.