I agree with autox fil. Think about it carefully. I regret doing so much to my zetec. Stuff like cam gears, udp, TB, and intake that I won't remove to sell it but don't add to its value.
If you REALLY want to mod it, maybe suspension, chip (if auto), lower temp thermostat, tranny cooler (if auto) and some audio. None of that is too hard to install or remove (suspension being the hardest) and will be your best bang for the buck.
