eh, I hate to sound mean, but that's pretty good for a c230 non-kompressor. you're driving a 3,500lb car with a naturally aspirated 4 cylinder!
not many options for performance upgrades for you beyond cold air intake system and complete exhaust kit. but with top-dollar investment on both, you're still looking at about another 20hp for around $2,000 investment. That's why the guy in the honda is in a honda. $2,000 gets him a big turbo and double the HP, plus exhaust and intake. But he's still in a honda (elitist of me, I know).
Your best bet, if more speed is really important to you, is to lose weight anywhere you can stand it. You also just slapped on a set of 17 or 18" rims, right? That's more metal and rubber = greater mass at greater circumference = engine does more work than ever to get them turning. This means better MPG because of fewer rotations to travel, but is also taxing your acceleration a bit because of the added weight on the wheels.
The best solution is to just not race. As George Washington said, "'Tis better to be thought a fool, than to open your mouth and remove all doubt." Let them wonder how fast you are. Don't ever let them know...