The question is why anyone would want to go to a theme park. It's paying money to stand in line and get passed by people who paid more money for the feeling of privilege they get passing you in line.
It depends on how you like to spend your time. We have been to Disneyland once, shortly after my older kid turned 8, for a birthday trip. We had 5 people, went for 2 days (with 2 nights in a hotel), and got the Southern Cal resident discount - this was several years ago. I'd always been pretty anti-Disney, WHY would you spend that money?
After the trip, well now I get it. I was pretty amazed at ALL THE THINGS. We went during the week (spring break), it was not spring break for any place nearby (was for Oregon, Colorado, and Idaho...saw a lot of people from there). Thus, the lines were not very long. We also went early, so managed to ride a couple of a our favorite rides 2 times back to back.
I was pretty much amazed at how clean, well run, and entertaining everything was. It's no wonder that it is expensive (plus: people are crazy about Disney). Squeaky clean, entertainment literally everywhere. It was FUN. I have a few friends (adults in their 60s) who have annual passes and go a LOT, and know all the tricks for when to go (time of year, and time of day). So if we ever decide to go back, I'll pump him for info. (My younger kid doesn't remember the trip, he was 1.5. My nieces and SIL LOVE Disney, go to Disney World a lot. They may be visiting this summer. If they do, we will likely go.)
Honestly though, my favorite theme park is Legoland. We go almost annually. Much cheaper than Disney (though further away for us). Shorter lines, fantastic things built out of legos to see. I love Legos, and I enjoy it. We aren't likely to go this year, but last year we went to the original one.
Given a choice of vacation, my very first choice is what we did over Thanksgiving - a few days in a remote cabin, no cell service, in a new place where we can hike during the day, and play games and drink hot cocoa at night. I love active vacations - beaches, hiking in the mountains or forests...however, I'm not the only member of the family. I'm happy to spend some time at a theme park occasionally.