I agree with that, even not being a car guy in any way, shape, or form. Plus, putting a few thousand miles on a $2,000 car will probably bring its residual value to something close to nothing, so selling it afterward will be worthless.
The other thing is, do you get free entry for life or something if you have a job at Geauga Lake? If I were Cedar Fair, it'd only be for the summer that you're an employee...I'd check that out if I were you. And if I misread it and you're taking this trip the same summer as your job, I have another question to ask: what is your boss going to say when you miss a week and a half of work to go ride roller coasters, especially for free on your company's tab?