What you need to understand, and what I believe Dave was trying to explain, is that going from 4 watts to a couple more isn't going to do anything. Even using your 2 watt radio, going from 2 to 4 isn't going to do anything. You're literally talking about 1/2 S-Unit on the receive end.
You basically need 4 times the power (6 dB) for 1 S-Unit on the receive end. So in a 4 watt CB, you would need to go to 16w to add just 1 S-Unit on the receive end. Peaking and tuning is not going to take a 4w radio and make it put out 16w. So is it worth it? Only you can make that decision. By and large, it's a waste of money, aside from perhaps boosting the audio.
If you're looking for more power, just get an amp or a radio that puts out more power, and save the money on a peak and tune.