Every dealer has their own policy when it comes to "Demos" etc. The car you are looking at may have been driven by the owner of the dealer, his wife, General Manager, who knows?
Some dealers only allow their cars to accumulate a few 100 miles before they park them, it varies.
As an owner of a '04 myself, I think the car is worth alot more than 18k, naturally. But, I suppose that's what they're going for.
It's true you can buy a new base model for around 18k, and I personally think that's a steal (for all that you're getting). But as you pointed out, if your wife can't drive a manual tranny, that's not a viable alternative either.
As 13K9 pointed out, if you live somewhere you get alot of snow, you may want to rethink your potential purchase.