Yes, the Space Grey probably does look good with all the Silver bits. We didn't have an option of an X-Line pack in the UK, just running boards. We did have the Edition Premium pack though, which included Silver grill, Chrome tailpipe, better wheels, Space Grey Interior Trim (See pic attached)
If you do go for black though, take a look at the Metallic black (Black Sapphire), rather than just the Black. We thought it looked much better.
I see your point about the pano roof, especially since a second hand X3 will be out of warranty.