Tony, I think you're dead on with buying the 300C. After all, you know where it's been; you know it's been cared for properly; and you already love the car. I didn't want to say it above - cause it's just not cool to knock someone's new ride - but I think the 300C is a helluva car - better than a CTS any day!
Plus, you'd be driving in style - every day - rather than having people look at you funny driving a Sante Fe.