I never used to get the Nav option...had always seemed like a rip off. Then had it on the last car purchased, my wife's Audi Q7. Learned to really love it. That said...comparatively I do not like the "NAV" on my Raptor at all...and in fact have hardly used it for navigation. Being hobbled without the ability to input changes while underway (can be overidden with aftermarket solutions), and not being too intuitive (like for simply pulling up a map...I know how to zoom in or out...but how do I scroll forward along my intended path, if I'm just using the map to see what's ahead...what road options exist?) So getting it for Navigation uses, my answer would be no. I got it almost entirely for the 7" screen with integration to all the other stuff on the car...and I thought it looked better...and the money didn't particularly concern me. While I occasionally use the Sirius, I almost always use streaming Bluetooth audio from my iPhone (Slacker, Pandora and Rhapsody). Would be nice if song/artist would integrate to the display and hopefully that happens. I think Sync is claiming it's possible, just needs the app development. At least steering wheel track control works so that works for me. I find myself using my iPhone on the fly for Nav...having wife or kids help if they're with me. So much easier. I use the Bluetooth handsfree phone and love it...having the caller info displayed is great...but the Raptor without the Nav probably still does that just fine.
So I guess the concise answer: don't get it for the Nav function. If I could get all the other system control on a touch screen and good, functional, intuitive Nav system on an aftermarket...that didn't make the dash look cobbled up, that would be my choice. At least now if something better does come out (like an iPad or BlackBerry PlayBook in the dash that integrates with Sync and HVAC) or whatever...at least I have a little more real estate to work with on the dash.