The standard system isn't terrible I agree; I can't comment on how it compares to other cars as I've had BMWs for many years now; but for £650 the HK upgrade is a steal, so much better than standard for the little added cost!
I don't think HK is spec'd that much though; the 2 dealers I visited while looking at the F30 didn't have any cars in stock for me to try it in (not even older used ones), and the salespeople I spoke to didn't have much experience of it and didn't know much about it, as if it's not something that's chosen much.
I think enthusiasts on forums are more likely to go more mad on the options list and be more bothered about getting the best, than e.g. a company car driver (sadly making up many 3 Series sales!) with a base spec, so perhaps all the talk on here about HK and HUD etc. isn't representative of the bigger picture? I could be wrong though, but my sales guy did say it's not spec'd very often, though it most definitely should be!
I was much more impressed with the F30’s standard system compared with the standard system in my 135i though. That really is bad, very thin-sounding and dull. I almost didn't go for the HK in the end, but I'm into my music so thought for the cost it was probably worth having. I'm sure I won't be disappointed