Not sure how sales tax works in your state, but the effective price at 6% tax is about 16,600. That's over 25% discount... If you are planning to keep the car for several years, I think buying new at this kind of deal makes good sense.
The Sonics do drop in value FAST, but if you get this big of a discount, that balances it out pretty well. Let's say its only worth 12k next year. That looks like a 10K one-year loss comparing it MSRP, but you only paid 16K plus some change for it, so its really a 4K loss and you get a very good warranty from a company that, in my experience, has treated me well.