I like my D610 - to the point where I sometimes go on about how much I like it too much. It does everything I want, photographically speaking, so to want something different seems unreasonable.
However, something I once read comes back to me. It went along the lines of 'The reasonable man is content to try to fit into the world around him, whereas the unreasonable man always tries to make the world fit him. Therefore all progress depends upon the unreasonable man.' I can't remember who said it, it might have been Carl Sagan, but it's always been my excuse for being unreasonable.
This unreasonableness currently manifest itself in my desire for a Leica M and a couple of lenses. I had one many years ago and I loved it but it was as unsuitable as an only camera (for me, at least) as a digital one would be today. And yet I still watch them on eBay. A tidy M9-P can be had for about £2k and a couple of Canadian lenses for, maybe, another £1500 the pair. £3500… Fortunately I don't have £3500, not even if I sold all of my sellable possessions would I have it. I still look though!
It's not GAS (Gear Acquisition Syndrome) because I am obsessed, these days, with a small outfit - if it doesn't fit in a Bilingham Hadley Pro I don't want it, but a Hadley Pro is just about made with with Leicas in mind!
I have even tried logic! My D610 will run rings round an M9 - resolution, dynamic range, low-light, battery life, maybe even build quality. I KNOW all this but I'd STILL love an M9-P!
Okay, so you have to go some to beat a 50mm Summicron (we won't mention Summilux or Noctilux - I can't even afford to dream about them!) but my Nikkor AF-S 50/1.4 is far better, in the real world, than you will ever be told in a review, easily better than me. If I want to go exotic (if? Of course I do…), half of the price of that used M9 will get me a brand new Nikkor 58/1.4 GN - and my wife probably wouldn't even notice.
But I still want one...