I didn't order the premium package on our 335i and have no concerns about not having the leather. Honestly, the Dakota leather on our X3 isn't very impressive at all. It's pretty stiff and doesn't feel that great and makes us sweat in the summer. Hasn't shown age after 2 years of use though which is a plus. I looked at some leatherette on the lot and it looked nearly identical to the Dakota leather. 90% of people will never now the difference.
Had a 2007 ML350 with MB's proprietary leatherette MB-tex and it still looked new after 125k miles of use. Also held up great to big dogs trouncing around in the 2nd row on an almost daily basis.