“lack of chivalry is not boorish”
Yep, it really is. Especially with a date whom you are presumably trying to impress with the idea that you would be potentially a loving and considerate husband. If you cannot be bothered to take one minute of your precious time to walk her to her door and see her safely in, why on earth should she ever believe you would take more of your precious time to be a good and considerate husband and father? Sorry fellas, you will never win with me on this one!!!!!! And you make it worse every time you try to come up with some rathionalization for the boorishness.
A rov who would use TZNIUS as a justification for not being a mensch, should maybe talk to another rov and get a different perspective. The only exception to this inyan is if a guy absolutely cannot get a parking spot anywhere and cannot leave the car standing where it is, but he should still get out of the car and watch her get inside her house or apartment door. Being a gentleman is part of derech eretz.