It's easy to ask this question to theme park aficionados like ourselves, but ask someone who likes theme parks but isn't so crazy on details and you'll get a whole 'nother answer.
Which is a hard thing to summarize to someone :)
It's like when people ask me: "what software do you use to design theme parks?" -- the same software that every other design industry uses. It's not some "secret software" or magic elixer that solves problems -- it's the collaboration of numerous talented people in multiple disciplines, focused on the same goal, that solves problems and creates magic.
The most pertinent "secret" I've ever discovered about attraction design are Mickey's Ten Commandments -- which aren't a secret, and apply to EVERY project we do EVERY DAY, no matter what park or attraction or part of the world we're working in.
That said, what I don't want to know is the plot. So, I avoid "spoilers" until after I've experienced an attraction (or a movie, for that matter). Nor do I want to know every single effect. I want to say, "how'd they do that?," at least some of the time. For instance, I avoided recaps/previews of what was exactly on HP & the Forbidden Journey until I rode it. I knew some things, including that it uses a Kuka arm, but knew neither the plot nor exactly how the arm would be used (brilliantly, I might add). Basically, I like knowing how it's done, but just tease me at the beginning. I can always learn more after I've tried it.
Why do you need to know? It is the same thing with magicians in that once you know, the trick is ruined. I really don't need to know how the trick works. You probably already know the tricks for the smaller or older attractions. The newer attractions are a mystery, but probably not that hard to crack. This is an issue of money and how much a company is willing to pay to make it work.
The secret that even Disney seems to not figure out is how to make a better park than Disneyland. They keep missing the mark with the exception of DisneySeas. Every other park is a disappointment.