Which wheels are you looking at buying? I highly recommend adding the flares and going with wider wheels, it really helps the look of the X5. You can probably get the flares, parts and install for around $400 out the door.

I say go for the 22" x 9.5" front and 22" x 11" rear setup with the wide 315 rear tires.

You can paint the plastic flares if you wish but they could chip over time if not prepped and painted properly and then also they won't match the rest of the black plastic mouldings on the bumpers and running boards.