Yeah, Knott's springs to mind. King's Dominion like I mentioned. King's Island. Cedar Point. Discovery Kingdom (soon). The Disneyland Paris Resort has two, again, like I mentioned. Great Adventure used to before they got rid of Chiller. They're not everywhere by any stretch of the imagination, but, having two launched coasters is totally realistic in a park of Alton's size. And given its unique restrictions, it would make a LOT of sense. A launched Wing Rider, for example, would be absolutely perfect. And awesome. A Maverick-esque coaster would be absolutely awesome as well.
It would have nothing on the stupidity of Canada's Wonderland getting another, just taller, B&M Hyper, for example. And it's no different to how loads of parks have more than one wooden coaster. Or more than one family coaster. Or more than one "standard" B&M that does loops. Or Great America having two Wild Mouse coasters.