Quality is not subjective they are definite lifts in sound, but the need is depending on circumstance?
If long distance cruiser and mainly on your own I can be swayed to the worth, its a nice settled environment and good audio is a great companion and you can set volume to its best level.
If do mainly shorter runs and regular carrier of passengers and for most part in a disturbed environment then its not worth the additional expense as benefit is lost in the surroundings.
my usual fayre is shorter runs and passengers and tend to listen to radio and get told to turn music down! when teenagers have Ipods plugged in (as my music taste is shocking obviously)
So not going to criticise the tech, the ones I have listened to are really decent but the standard set up is not rubbish, you get some decent clarity and pitch and so its not worth the expense for me, so its more about do you want to impress with your high end tech and can afford to (previously had Bose in Audi and always got comments to the speaker grills) or are that long mileage cruiser - outside of that, IMO not worth the additional