well the front bumper IS lower than standard and from MY own experience with a front lip which IS lower than the Nismo's... it is definitely not that practical, but not because of speedbumps which were surprisingly negotiated very well (many kinds of different heights) but more directly related to multistorey car parks RAMPS, and steep slopes (ie my drive, which I did modify to suit my kit )
Of course I can take off the front lip, you can't just take off the bumper