The front of the XJS always looked a bit empty and unplanned to me. Not that I'm any smarter than Mr. Lyons designers, but I chose to make a couple of changes.
Chrome on the leading edge of the grill cross bars hi-lighted them slightly.
Same below the bumper, but if you look closely at the air intake below the bumper you'll see an indentation on each side that looked like a continuation of the grill shape. I chose to fill those indents with lights, just like the current Jag sedans. After much searching for ones that would fit, I came across a pair of PT Cruiser lights that bolt right in.