Kind of funny you one of you mention Paramount Canada's Wonderland and the other mentions Darien Lake as 2 parks who don't have any competition when the fact is... both compete with each other!
Truth is, they aren't all that far away from each other. If most of Darien Lake's locals live in the general Western New York area, which consists of Buffalo & Niagara Falls, then you are only a mere 30-45 minutes from Darien Lake and a 90 minute drive from Canada's Wonderland.
That's competition right there!!
It's a little distant from those who travel from Toronto or it's northern suburbs, but not all that far especially if they stay at Darien Lake's campground for the weekend!
Anyway, both of those parks not only compete against each other, but they also go against other smaller/medium sized parks such as Marineland, Canada... Martin's Fantasy Island... Seabreeze (as sad as that may seem)... and to a much lesser extent, Waldameer Park (for SFDL)... Wet 'N' Wild (PCW & SFDL have a water park. Why pay full admission just for waterpark when you got WNW?)!
It may not be competition as much as just the park operators and CEO plan of attack and seeing if it's the right time for expansion.
Maybe the owners think that their crowds (and percentage of increase/decrease from the years past) are good enough that they don't need to add any significant improvements, despite what others may want.
I wish it wasn't true, but that's my guess.
When the time is right, they'll use their capital investments on something good.