Will an HD Radio improve my car audio that much?.....

With road noise and such with the factory system I doubt you will notice a huge difference in sound quality. It will be better, but probably marginally noticeable. That is unless the Sebring is more sound insulated than I imagine or has a really high end factory system.

On the other hand, in my opinion the sound quality is not the primary reason to get an HD radio. For me the much wider variety of music available on the sub-channels with NO COMMERCIALS and VERY LIMITED TALKING is by far the most compelling feature.

If you like chatter and mainstream radio already, I would say for the average auto the sound quality aspect is not a significant factor in recommending HD radio adoption.

I agree that road noise isolation in an automotive environment , is key to enjoying the POTENTIAL for improved dynamics that HD Radio is designed to illicit. You should benefit from such sound options by default but it will depend on the stations in your market and how they honor the technology individually. I say that because it is up to the individual radio stations to remain true to the reduced compression that HD Radio in digital mode can make allowances for due to the total elimination of analog signal-noise anomalies such as mufti-path picket fencing and stereo noise and blending artifacts not apparent with pure digital capture of this signal. The "philosophic sonic environmental landscape" that HD radio was to invoke, not all are embracing as they once did. Sometimes the "Loudness directive" for their main channel analog audio is merely duplicated in their Digital audio equivalent. It remains up to those the program the station's signature audio to take advantage of the more relaxed "cleaner sound that HD radio offers. That affords the distinctive attributes that make HD radio worth buying in addition to secondary channels that always seem to suffer from derivative digital audio compression rates and rendering more metallic audio then their main channel counterparts.

I'm a fan of HD Radio more for the extra content rather than the audio quality, but there is an improvement in quality that even my untrained ears can detect. But, your mileage may vary. I do hear the difference when my radio drops the digital and falls back to the analog. One of the best examples is actually - believe it or not - during talk radio when someone calls in and is on the telephone. They sound much better on HD than analog. Go figure :b

But the sound quality you'll experience is a blend of several things in your car. Not just the head unit, but your speakers, interference from the electrical system, the quality of your car's antenna, the acoustics of the cabin, and where you are geographically in relation to the stations you're listening to. Will you experience an improvement in sound quality on analog stations just by replacing the head unit? Maybe, but it might not be a big one. That depends on how good the existing head unit is, and what you replace it with -- but I wouldn't expect a miracle here.

Are you just looking to improve sound quality? Or are you looking to add features (like the CD player and/or the ability to plug in a flash drive or phone or something?) If your goal is purely sound quality, you'd probably be better off investing in better speakers maybe. If you're looking for features, go for the features and while you're at it get a head unit with HD Radio.