Depends on your definition of quality and how much you value uniqueness - if you only ever visit your home park, no matter how much you love coasters, than does it matter if every park from here to doomsday has a clone of its rides? Personally, I love unique rides rather than cookie-cutters, but there's something to be said for coasters that are becoming staples in parks, something that delivers a good (not necessarily great, but good and still fun) ride, so long as that is not the only coaster at the park.
I'd be willing to wager that most visitors to parks are not hard-core coaster enthusiasts and rarely travel to other parks solely to ride coasters, so the "quantity" issue wouldn't arise. And if you haven't been on better, neither would the "quality"! :)
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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/index.html