Glad at least you understood what i was saying. Was trying to work out what i was saying that didnt make sense to Scott.
Im not really following much of what you are saying, but i would argue that in many cases the theme is DEFINITELY chosen prior to the ride being chosen.
If i was the CEO of a theme park and wanted to open a new attraction, i'd take a look at my park, get an idea of what area of the park (theme) i wanted to incorporate the ride into and then choose a ride based on that theme (which could be age-dependent, size dependent, cost dependent).
I wouldnt just go, hmmm ... i want a Mega Coaster, lets order it. And then afterwards think hmmm, the only place i can fit it in is Wiggle World.
When they opened the Harry Potter Themed World in the US, they didnt choose a roller coaster and then think, you know what - that kind of seems like a 'wizard' like ride, lets build a Harry Potter world around it. They thought "we have a great theme idea - a Harry Potter world with Harry Potter themed attractions - now what rides would fit in with this"