Replacing the fabric inserts is a nice touch. Some aftermarket leather seating kits even come with matching panels for the doors (e.g. Katzkin). If you want to go a step further and paint portions of the interior plastic and vinyl to match your seat covers, take a look at Dupli-color products. They have paints made specifically for this purpose, although you might be able to find better paints out there (I haven't used Dupli-color personally, so I can't vouch for them).