Rear locker isn't a necessity by any means. We've run plenty of trail here in Colorado without the rear locker with no issues. A rear locker would be some help, I am sure. The other beauty of the $750 is that you get a full-size tire and wheel for a spare, (about a $1000 value in itself), and the prospect of increased resale value.
To me, on an ordered car, it turns into a done deal.