I replaced the buckets in mine with a set from a Fiero (speakers in headrest). I saw a really nice lower door panel, had a really nice speaker pod built into it.
You could also upholster the dash and door panels.. That'll let you change colors and give a cozier feel to it. If you don't have a console (floor or overhead), you could add one of those. Sex lights under the dash are always a classy touch.