I was in the same position recently and switched from D300 to the D600. After you give your son the 16-85 you will have to only sell two lenses which can be both compensated by the Nikon 60 2.8 AF-S for the D600. As for should you switch or not I guess it all depends on your shooting needs and interest in photography.
I miss the fps from the D300 but other than that the D600 is miles better on every other level particularly DR, IQ and ISO performance. Build quality is great and suits me better since I had a surgery in my left wrist but most would agree that the D300 has a superior build quality and manual controls. AF is great though might not be suitable for all people due to the fact that AF points are concentrated in the middle, but that doesn't bother me at all. I used to bracket 7-9 shots but I don't miss that now due to the incredible DR in the D600.
I had to sell the Tokina 11-16 (replaced by a Sigma 12-24), the 35 1.8G (replaced by 50 1.8G) and the Tamron 17-50 2.8 (replaced by a Tamron 28-70 2.8). I added a Nikon 28 1.8G, a Rokinon 85 1.4 and a Nikon 105 2.5 AIS. These manual lenses are perfect for the great video on the D600.