In the past, I've replaced both front and rear axels from nutted to QR. It's easiest to get new axels with cones and lock nuts, and of course the skewers. You may also have to get new bearings, but it can be done in about an hour or so.
And another vote for the hitch rack. Nothing touches your car, and it will no come off(if you put it on right), it's easy to lock you bikes to your car, you also don't have to lift them over your head. The one I have sways a little, but it's nothing to worry about.