I tried the speaker route first in my wife's '94. FYI- The wagon has 4" in the dash, 3.5" in the rear doors, and 6" subs in the front doors. I replaced the front dash and rear door speakers with Infinity speakers. The subs were and still are fine. Within one year, three of the four Infinity speakers blew. My guess as to why this happened is the factory system is a 2 ohm setup. Putting in the 4 ohm speakers required pushing the lousy factory amp too hard, resulting in trashing the Infinity speakers. Either way, it was less than ideal and never really sounded very good.

So...two days ago I decided to bite the bullet and get my wife off my back over her lack of tunes. Went with an Alpine CDM7871 head unit that interfaces with her 6 disc changer. The head unit cranks out 21 watts RMS. This was plenty for the Polk 4" up front and the 3.5 Infinity in the rear. I went with the polk up front after hearing them against 4" Infinity's.

This left the subs without attention. The Alpine unit has three pre-amp outlets, which allows a dedicated sub woofer amp. I put in a small MTX 4122 Amp which provides 80 WATTS RMS @ 2 ohm to each sub.

The end result is something that is much improved over the factory system, even when the car was new. Honestly, I am quite amazed how well it sounds. Total cost of the above work was about $800 installed at Circuit City.
Best of luck in your journey...