The cams were also redesigned in the '07 model to correct cam lean. I love mine and let my buddy shoot it today. He has a Matthews Switchback XT and had never shot one before and loved it.
You'r emaking a good choice buying a new one and outfitting it with what you want. Even if you paid the $550 you might swap everything out on it and only saving $100 on a used bow. You might be saving less depending on the cam price.