I think if you do alot of driving on freeways and stuff...
Nothing worse than wind noise and when you turn up the volume and the sounds start to distort.
It's definitely worth the investment. For me I gave up the sun roof for the HK.. Coz for me I didnt see how I was goign to enjoy the music with the roof open, so it was actually a savings lol. 2.5k sunroof for a 1k+ HK system.