Should I buy the SDARS\HD-Radio package with a new car?

So I'm looking for a new car and all the manufactures (Land Rover and Mercedes) I'm looking at show the Sirius Satellite OEM radio as an extra 700 to 800 bucks. What are you really getting for that? A different radio?

Then if I activate that OEM radio when I sell the car I'll have some kind of transfer fee or something I imagine? Maybe I'd be better to just go with a portable and then I can move it car to car. But I don't want some half-azz wires running all over the car. Thoughts?