it is just that the stock HU has like 40 watts total. you can get a very small amp, weighs like 4-5 lbs. and no sub. so you would have a total wieght gain of 6-10 lbs....

if you really are worried about weight, get new wheels, brakeman rotors, loose the AC, DriveShaftShop driveshaft, and keep the fuel below the 1/2 way mark...

have you painted the intercooler black yet?