I think it all depends on how much you listen to audio while driving, and of course, it, as others have said, is very subjective. The HK adds two tweets in the back, and the dash center speaker. Plus, the amp goes from 180W to 340W and all the drivers are upgraded.
We got the HK upgrade in the X1 because the wife listens to music all the time, and she LOVES it over the stock radio in my 135i. I've got the stock radio in 135i because I don't listen to music while driving.
However, for the Xenons, I, personally think they are a MUST have item. I will not buy another vehicle without them.
Here is a thread discussing the audio: