The caps dont' bring out the base -they supress it in the door speakers so the door speakers sound better. THEN you turn up the bass, which is blocked from the door speakers but allowed to pass to the rear ones.

So, IN EFFECT, the caps DO "allow more base" in that they allow you to turn the base up without it getting into the door speakers and ruining their fidelity.

I think 270 is a good value, I believe I put 330s in my car, but still.