I would recommend late August and Early Sept. (try to avoid Labor Day weekend). Bonus Weekends are a good time to go, too. In reference to your question about Millennium Mania, only some rides are open. I believe that they were MF, Magnum, Power Tower, Mantis, and Raptor last year. (Someone correct me if I am wrong). The price was $20 last year and there was walk-ons for everything open.
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