With the coming and continued investment by Cedar Fair, I don't see why new trains are a waste of money. Valleyfair invested ten million in Wild Thing when it was built, and it's now one of the more boring coasters in the park. With Valleyfair's limited size, every ride has to count, and while flats are more easily placed and removed, rollercoasters stay for decades.
Wild Thing takes up a significant amount of room in the turnaround alone. The ride experience should justify the space used and the money spent, and it currently falls short. Trains that at least let you experience the ride at its possible best can help. Chance Morgan hypers are about speed (says so on the Chance website) and Wild Thing doesn't really feel fast when you ride in a bathtub that shields you from the chest down. In fact, in parts it feels downright slow. But according to the stats the ride is not slow. Riders are prevented from feeling the speed. Easy fix here, thankfully--Lightning Run trains, lower profile and better restraints! And made by the same company for the same track, no fuss no muss. They would be amazing on a coaster built to be fast.
Just because other parks seem to be fine with old trains doesn't mean that they are. Steel Dragon switched and the ride experience improved. Why can't Valleyfair be the innovator in the USA and do something different?
And I don't see how improving the attractions you have will prevent great future development. The next two years are going to be waterpark improvements anyway from what has been gathered, so why not improve Wild Thing so the dry park has something too? The trains will not steal a potential new coaster out of the investment budget, that's absurd. They're spending how much this year on waterslides--several million (I think 8)?
And regarding Vortex conversions, I am aware of that. But if successful, they will start changing trains on other kinds of coasters to keep them palatable (think discount coaster wars) so I won't rule out train replacements on other coaster types.
I am sorry, there is no quantifiable evidence to support anything you stated in your post. While you, PERSONALLY, might feel that the ride is now "one of the more boring coasters in the park," rider turnstyle clicks do not support your hypothesis. Also there is no proof that the ride experience would be improved upon with different style trains. The fact of the matter is that this is Cedar Fair. The trains current on the coaster work just fine. They're not hindering the ride in anyway and the turnstyle clicks do not warrant different trains.
As far as your last paragraph - please explain to me how spending money on new trains will not take away potential money for future projects? Do you honestly think that the money for new trains will just come out of thin air and will be in addition to any money that would go towards new projects? It won't happen that way - trust me. I realize Cedar Fair has earmarked the park for growth, but let's not just throw money at things that don't need to be fixed just because some one has a flashier train than the one that you currently have