My NAS will be OK for a while when my 610 comes in tomorrow. For how long who knows?? I am already deciding to sell or trade my 300s for another 610. I won't know till I see the proof. I am still lacking a good tripod, a 24-75 and a good birding lens.
I think I mentioned it in another thread that I didn't end up using my D300 for a year after going FX and I've now replaced it with a D7100. Because the D7100 is better at some things than either the D610 or D800 I've actually been using it quite a bit. I suspect a second D610 may become a bit of an ornament. If I was a pro I may have a different view on that, but as an amateur I can't justify pure spares. I don't have any DX lenses as I'm covered from 16mm up with the FX stuff.