[oem4me]

Well, by leaving it alone you're not exactly sparing it from anything it hasn't been through before. Paint, interior, and bedwood are pretty much the key "originality" items that make or break a survivor. Untouched mechanics are indeed a major bonus that come with an unmolested vehicle, but it's the body/sheet metal and cosmetics that really set one apart from others.
I personally would do as little as possible, but that's just me. No sin in doing what makes you happy on this one.