Now I'm not a professionnal, but I've work on my friends rally car and I say just make sure no grass gets in there. If you buy a prefabricated skid-plate for your x-terra, couldn't you make additionnal plates to make sure no grass gets in?
Anyway I say it's better to have a skid plate and take certain precautions, then to be a wuss about it and not put one on, right?
