I understand your point, but for instance all of the additions you mention rides installed before 2000 with a very different leadership team for Cedar Fair and without all of the former Paramount Parks acquired.
For instance, Shivering Timbers was built before Cedar Fair even bought Michigan's Adventure. The same goes for Hercules at Dorney, it was built before Cedar Fair took over the park. Dorney, Valleyfair, and WoF all got a package deal with the Morgan hyper coasters and were a much bigger part of the Cedar Fair chain before the Paramount parks were bought. You can tell by the additions to the park since 2007 what parks are receiving the big ticket rides. For instance Kings Dominion, Cedar Point, Kings Island, Carowinds, and Canadas Wonderland have all received 20million dollar plus rides since they were acquired because those are the top visited parks. Knott's might not be included but it is, I believe at least the highest attended park in the chain. I mean WoF did receive Patriot which is a larger investment, but that was before the Paramount parks were acquired. But for a park to support a giga coaster of that size when the park doesn't hit a million visitors a year (according to 2011) is pretty unrealistic in my opinion.
Bottom line is that they could always get one, but chances are we won't see it because an investment of that size in the Cedar Fair chain could be much better spent at another park business wise. And if they ever did, it would probably be a long ways off if they are still part of the chain.
But I mean this report shows the distribution pretty well : http://cf.wddnsweb2.wddonline.net/_upload/pressreleases/final%20funforward%20presentation%20-%20with%20ebitda%20reconciliation.pdf