I would surmise that the luggage rack was an add on. As to value, i don't really think it would add value. I realllly don't care for em myself. I look at it this way: would you add a luggage rack to a '69 Jag XKE? Probably nope.
The "correct" luggage racks were from AMCO, now out of production. There are a few that pop up on EBAY every now and then, make sure you get all the hard ware. As for Jags with them, I have seen far more Jags WITH racks than without, as a Jag does have a whole lot of trunck space to begin with. I also like the Sportwagon with a roof rack, dresses it out nicely.