It's a rip off really. Get yourself a good sealant (Zaino, Menzerna, etc.) and apply it yourself once every 6 months, or more as needed. The only benefit with the Simoniz is the warranty, if you're really into that, but realistically, you'll be hard pressed to get anything out of it (i.e. your time spent to fight over it is not worth it).
Lastly, what exactly are they going to do? Are they first going to strip any wax of the car, then clay it thoroughly, then do any paint correction necessary, polish, then apply the Simoniz? I really doubt it. They'll just have their "shop" slap it on like some regular old wax and call it good, letting all the crap that's there be trapped underneath it.
If you can swing it or care to for that matter, pay the $400 per year and get a proper professional detail, and do the weekly/monthly maintenance of the finish yourself.