If you pay for it, ask them for a year deal and only accept one that is around $90/year. It will take a little while for them to offer it but at some point they should (or call back and do it again until it's offered). Sirius is a _terrible_ company when it comes to price. They try to screw customers over with higher prices and wait for them to haggle the price down.
I have had Sat radio in my vehicle's for about 15 years now. I just can't go back to FM. I dropped it in my truck as I don't drive it that much and I added an aftermarket radio where I can stream Pandora (and it would cost another $150 to add the sat radio hardware). I think the sound quality is on par with a CD. It's very nice to be able to listen to a certain channel no matter where you are. Also, I think the programming is very good, that is, it's nice to be able to pick many different types of music channels and only listen to that type of programming. Is it worth $7/month? Yes. Is it worth $14/month? No.