You should get some custom seat covers...check this site out, these covers look like you've had the seats upholstered:
www.wetokole.com
Also, get a different gauge face plate, gauge needles, rear view mirror, floor mats (or custom carpeting). You can also get this paint stuff that changes the inside color of your doors and dash and like material. Get creative. You could get a different steering wheel. Just a few ideas for you, hope it helps a little bit!!!