Just another opinion for what it's worth. I'd be inclined to leave the black bumper cover. As already noted, if you could get an exact match among roof rails, sidesteps, and bumper cover, it would tie together the three elements. But I'm guessing you'll have three slightly different color surfaces that look like they're "trying" to match.
Personally, I rather like the black bumper treatment (and lower cladding) of the LX and EX. And that's coming from someone who just purchased an SX with the . (Got a tremendous deal on a barely used 2012 SX with 7,000 miles and just couldn't justify spending $2000+ more for an equivalent 2013 EX.)
With your white car, I think the black/white combo is especially striking.