I would always pay for upgraded sound system in cars and always have.
They’re not all good, though.
The Harman Kardon system in the F3X BMWs is decent once you sort out the EQ and remove the excessive ~200 Hz frequency.
The B&O system in my S5 was abysmal, and I spent a further £1000 trying to sort it out. Still wasn’t happy with it.
The HiFi system in my 135i is REALLY good. There’s no passive, or active, crossover on the front mid/tweeter though, so you do get a bit of distortion at higher volumes with some songs. However, I did upgrade the amplifier on this, which has super powerful software, allowing for a lot of EQ and time alignment. Best sounding system I’ve had in a car so far.
My Boxster has the Bose system, which tonally is quite decent. However the tweeters are a little shouty at higher volume. Only car I regularly turn down the sound though to listen to the flat 6.