First up 'worth' is very much objective as is anything audio..
A car is hardly the place to expect HiFi audio. It's a tine box rumbling along an imperfect surface..
The standard audio in my first RC was perfectly acceptable (for an in car system) and the ML in my second RC is definitely an improvement on that. Is it worth the £1000 price tag? Well as a percentage of the overall purchase price, yes. As a stand alone cost no way..
Just about anything can be retro-fitted to vehicles these days but the complexity and the knock on costs are very much greater. Only the person paying the bill can assess it's worth to them.