Anything you buy is going to run circles around the now-over-fifteen-year-old stuff in our cars. If you are willing to spend NOT a lot of money, you can walk away with better sound, Bluetooth compatibility, more power and all you could ask for.

I like Kenwood/JVC stuff, but I work there, so I am hardly an unbiased advisor.
Three years ago last month, I bought a discontinued JVC RD660 AM/FM/CD/USB head for $85 at Best Buy (same cost as thru the company discount program) and put it in my SE. Night and day difference over the factory stuff. Mine is a base, so I added wiring and rear speakers. I now have true four channel sound and the ability to drive the rears with base only - sounds SO much better.



Need to pick up a good amp and beef things up.... maybe I will when it goes below 80F outside...