I would consider dark rides to be "considerable" additions, and I could see them popping up at the smaller parks when the larger ones are getting coasters. I think at these regional amusement parks, the interactive dark ride is one of very few rides that can be more impactful (on marketing, sales, and customer happiness) than a major roller coaster. Dorney Park is definitely getting either a thrill ride, water park addition, dark ride, or GCI. I just also doubt that Cedar Fair would purchase a singular GCI coaster when a) the older ones are getting RMCed, b) they couldn't get a deal because they would only buy 1, and c) in the competitive PA theme park market, one could say that a GCI coaster wouldn't make any difference, as the racing GCI at Hersheypark is much more impressive. My Prediction: Dorney gets a Delirium thrill ride made by Mondial.
Sadly and truthly, Dorney Park is in the bottom-2 theme parks for Cedar Fair. It is a bad park in a heavy market, and MI adventure, is just in the middle of nowhere. Cedar Fair values sales much more than what would make a park better, and trust me: my home parks could use some additions too.