In defense of Disney, very few of their rides are exactly the same. Things like Space Mountain, Big Thunder Mountain, Pirates, even the Jungle Cruise have major differences from park to park. There was a great article in Disney Magazine last year detailing the differences at their four Magic Kingdom parks. On my first trip to Disneyland last year (after 27 years of visiting WDW)I was amazed at how barely anything was the same. (Exceptions being the Dumbo ride, Carousel, a few others)
Personally, I'm a little let down when I see too many EXACT clones at parks, mainly because it denies me the chance for a NEW experience. But as many have pointed out, not many people travel cross country (and beyond) to see theme parks.
I think it's more important that neighboring parks don't own the same clones. THAT could be frustrating to people.
As for Cedar Fair, their empire is an odd lot to begin with, unlike planned chains theirs sorta happened by seeking out venues through friendly acquistions (i.e. Knott's Berry Farm). This gives them a definite advantage in uniqueness... Half the ideas weren't theirs in the first place.
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"You have to scale a lot of lift hills to coast easily..."
Jason