Why only 30W?
Most car radios are advertised to deliver 200 Whats. They actually deliver about 14 Watts RMS continuously to four (they have 4 channels) 4 ohm speakers over the 20Hz to 20kHz frequency band with low distortion.
If your car radio has four channels and your speakers are each 4 ohms then already the radio produces 56 Watts, or 200 Whats.
If you double the power then the sound is only a little louder. Ten times the power sounds twice as loud.