If you already have a 2 way driver in your door, the main advantage of getting tweeters is to better pick up the 3000Hz+ area (tweeters on 2 ways are usually lacking a bit) and move your sound stage up some. Get you a crossover (active preferably) and some tweeters with great on axis response and mound them in the corners of the dash pointing towards the dome light. This is a good place to start for good imaging. If you get an active X-over than if you ever want to upgrade your midbass, just replace the door speakers with true midbass drivers.
2000 Mazda B3000 TL Edition 2wd
-Gibson Exhaust- -Gangsta' Tint- -31" A/T's- -2 15" SI Mags- -Sundown SAZ-1500D- -LSD- -Torsion Bars Maxed-
*Eventually: Head Lights, More Tint, 5.0 swap, Murdered, Tube Bumpers, Off Road Lights, Body Lift, Better Stereo, More...