If this is the turbo Baja (EJ257), I'm REALLY surprised she has not blown something as of yet. If it's an NA car, they can stand up to quite a bit of abuse (factory rec'd OCI is 7500 miles), but never changing oil will put any engine six feet under.
IMHO, I would stick with a couple short OCI's-I'd say about 3k max. I'd try to use a high mileage oil as well, or something else high quality.
Best of luck to you man. Get it back on a regular changing interval, and it might just last her a nice long while.
Value? I'd say anywhere from $10-15k, depending on model and mileage.