Having been driving a few modern cars just recently, I considered starting a similar thread. In the last few weeks I've driven a Hyundai i10 (hire car), a Mercedes E350 Cabrio and currently have an Audi S6 (standard Audi A6 body but with a 439bhp Lamborghini 5.2 litre V10 under the bonnet) parked outside. All have lots of modern driver aids, many of which will become compulsory in a couple of years and it set me thinking which would I like. Obviously all have a screen in the dash dealing with navigation, radio, media, audio settings and various other things that can be controlled by the driver but even at under 10 years old, the nav on both the Merc and Audi are getting a bit dated.
Reversing camera, yup, but that can easily be added to any car as can reversing sensors.
Then there are the driver aids, things like adaptive cruise control, brake assist, blind spot monitoring, lane departure warning, etc. I never use cruise control, preferring to to control my cruise speed with my right foot and on both that have it, it had been turned off anyway, as had the brake assist. The owner of the Merc told me that adaptive cruise was a pain as it would slow down if it saw a car in front of you travelling slower. Fine unless you intended to overtake that slower car because it expected you to indicate to pull out to overtake but if you were already in the overtaking lane, it had to be overridden.
The lane departure warning on the Merc and Hyundai would cause the steering wheel to shudder (and reduce the power assistance on the Hyundai so it felt like your wheels were in a rut) if it detected that you were drifting out of your lane. The only way to stop it is to indicate to pull out to overtake but you still had to indicate when you wanted to pull back in. However, if you indicated to pull in while the car you had overtaken was still in view of the blind spot detection in the rear view mirrors it got grossly offended and caused the steering wheel to shudder and it would beep loudly at you too!
I thought the blind spot warning would be useful and it is to a degree but I found it makes you lazy. As a big red triangle appears in the mirror if there is someone in your blind spot, I found I was relying on that rather than looking over my shoulder (what is known in motorcycle circles as the lifesaver), so while useful, not something I would consider an essential. At the end of the day there is no substitute for the Mk1 eyeball.
The Merc also had automatic dip beam which I must admit I really liked. Put the lights on main beam and if it detected another light coming towards you, they automatically dipped. Initially I thought the system may not dip when coming up behind another vehicle so I would blind them with the lights in their mirrors, but no, it detected them and dipped the lights. The only time it was fooled was on a section of road with Armco on the central reservation which obscured the other vehicles lights but not their windscreen so it didn't dip the lights but the oncoming driver got the full benefit of a pair of HID lights in his face. However, I did drive that car back from the south of France where there is hardly any traffic at night so I doubt it would be that useful in the UK when the roads are so crowded, even at night, you rarely get chance to use main beam anyway.
Although I've got my stereo as good as I can expect without spending a fortune (Kenwood DAB head unit with Bluetooth, JBL speakers in place of the originals and a powered sub under my seat), the Harmon Kardon system in the Merc and the Bose system in the Audi are absolutely amazing, so that would definitely be on my shopping list if it could be fitted without taking up any more space.
As Dave says, more power but having got out of the Audi yesterday and straight into mine, it still didn't feel underpowered, although I wasn't trying to break any records (which the Audi probably can do and sounds glorious when given some welly!).
So the bottom line is that while these modern driver aids may be useful, there isn't really any of them I would insist on having, except maybe the blind spot monitoring in the mirrors.