If everything checks out as commented above... would be worth having at a reasonable price. And also depends on what you plan on doing with it.
Me personally, I've never considered XJ's to be rare by any stretch as they made so many of them all around the world between 84 and 01.
That doesn't mean this one might not be a very nice preserved example...but IMHO... low mileage and showroom condition only = big $$$$ IF it's a desirable model and very few of them were produced.
Just because someone slaps on a "collector" tag to something might only be in their opinion. Just my 2 cents... still a nice looking XJ