Nope, if you want to change the sound in your car, you will pretty much have to gut the system.
Your 230's stereo is in the crappy department for a Mercedes! My friend has a 99 C230k and the stereo is relatively clear, but the bass is what's really hurting. So I know how you feel.
I have the Bose in me 95 C280, and it is definitly better than the standard stereo for the 202.
But the Bose still lacked some bass... so here's what I did:
Bought a 10 inch sub and a box (sub goes in box [enclosure]), and I bought a 250W amp. I then had the guys install the sub and amp. The install costs more than normal, because extra wiring is needed because of the more advanced Mercedes stereos (have to bypass factory amps). But the bass is not overwhelming or "ghetto" or anything of the sort, just a nice solid thump; of course you can always adjust the level if desired.
Anyway, I had this done @ Circuit City for a little over $500. I am now totally satisfied with the stereo... it's very impressing.
What my point is... Your C230's stereo isn't all that bad... but one of the major downsides is the bass, or lack there of! So if you did what I did (sub and amp), I think you might be satisfied... only because your stereo still gives fair still more than fair clarity at high volumes. But it would cost about $500. (And make sure the place you go to is very familiar with Mercedes...!!
Sound like a good idea for your needs? Good luck and hope this helps!!