Yeah, I had (actually still have) a 1992 Explorer with almost 200,000 miles on it with roof rails and I've never used them for anything. They just made it more difficult to wax the roof. Although the effect is probably minuscule, they also have a negative impact on MPG at highway speeds.

If you actually have a use for them, such as transporting skis or other stuff, or like the look, then it makes sense. But for people like me who don't have a use and prefer a more uncluttered look, it's great BMW now gives a choice. And at $100, that might be a record low price for a BMW vehicle build option (other than the zero cost ones, which I think of more as choices, rather than options)!

P.S. I subsequently did a search and found this:

Does My Roof Rack Affect My Gas Mileage? : Planet Green

I doubt just the rails would have nearly as much impact as an empty rack with crossbars and stuff, but based on my Engineering days back in college, I do know that even small changes into the airflow around objects are hard to predict and can have surprising impact if it makes a boundary layer detach early or adds turbulence. It would be interesting to see some wind tunnel data... I'll bet BMW has done this internally.