I don't think they outright compete with one another, but more compete for the media attention which adds up to more publicity and more profit for them. The media is always attracted to the new, better, and unusual, so I think we'll begin to see some very unusual designs and innovations, rather than higher/faster/steeper. As if we haven't started that route already with Son of Beast, Stealth, etc. The weirder it gets, the more I'll want to ride!
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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/index.html