each to their own, but in my opinion it was worth every penny - although it must be said we didn't get it as a factory option. I had sourced the RNS-510 from an eBay vendor in Lithuania to put into my B6 Passat. When I traded in the Passat, I transferred the RNS-510 to my wife's Tiguan (a straightforward job).
It's a good sat nav, the touch screen is really nice to use, and it should throw information into your instrument cluster display - like nav directions, "next turn"etc. The real selling point is the "integrated" look and feel.
Also from a security perspective you're much more likely to have some scumbag break a window to snatch your Garmin or Tomtom or whatever other portable SatNav device you may have, than to try and disassemble your dash and take the RNS-510.