I would not patch any nail holes.  The new owners might not have time to paint right away, and if the holes are small, they might use them for their own pictures to feel more at home until they have time to paint.

When I bought my first house, the owners left a nice little gift basket and a note for me on the kitchen counter. They told me how they had fixed up the house and loved it in the 13 years they lived there, and hoped I'd love it just as much. (the house was condemned when they bought it--single mom with 3 kids who let the house go to pot and let the kids run all around the neighborhood unsupervised while she drank and watched TV, I heard later from the neighbors--and the new owners at the time did a wonderful job fixing it up) The basket included a small plant, a bar of nice soap, a bottle of sparkling white grape juice, and some nice candies.  I loved that basket and thought it was a really nice touch.  Personally I'd rather have a nice little gift basket than patched nail holes or even a clean floor--I always clean new living quarters thoroughly myself before moving in.