I have replaced ALL of the audio equipment in my 96 for various reasons (blown speakers, CD changer went out, no lighting on radio, etc.). However, I would recommend leaving as much stock equipment as possible simply for the reason that once you start replacing its hard to know where to quit and the stock equipment sounds great in general. I think you have the right idea with only replacing the speakers. A couple of things to keep in mind:
-Make sure that the after-market speakers match the ohm load of the factory speakers. (Its usually printed on the back of the factory speaker 2,4,8, or 10 ohm. The ohm symbol looks like an upside down horse shoe.) Failure to do this may cause damage to your amplifier of head unit.
-Your subwoofer is a "free air" style woofer. Building an enclosure around it will not make much of a difference. just make sure that the one you replace it with is free air capable. There are other options if you are interested...
-Even though these cars come sound sealed very well, there are options to suppressing exterior sound. The product I used was dynamat. It is a sticky material with sort of an aluminum backing. I lined all of my doors and trunk with it. There are a few different companies that produce a similar product. You can also use spray on bed liner. (Sounds silly but its effective).
Good luck!
