The D610 is a bit of a stupid camera, really. You can get a D600 instead and its basically the same camera, just a lot cheaper and if there are any problems with sensor dust, Nikon will fix them anyway.
I realize the 750 is the newer and has some upgrades compared to the 610 but wondering if it's worth the $500 difference.
Yes.
The D750 has a sh***load of improvements that should have been in the D600 already.
The D600 for example has a disappointing autofocus. The D750 has the best autofocus you can get from Nikon right now.
The D750 has a flipscreen, uber useful for video, macro, or simply shooting from the hip.
The D750 can show you the focus point in 100% magnification in a single click ... that alone is extremely valueable (and I'm angry at Nikon that they dont offer an upgrade for the D600/D610 so they can have that too).
The D750 is also smaller, more lightweight, has a better grip, builtin WiFi, ... etc etc etc.
I still have my D600 and I'll probably wait for the next generation, but if I would get a new camera - the D750 is a nobrainer.
And its not 500$ difference ... its a ~20% difference. If you buy a camera for 20$ or one for 520$ is a HUGE difference. If you buy a camera for 20000$ or one for 20500$ is not. Thus its in percent, not in absolute money.
If I was to set them up with the same lens and take the same shot would I see a difference?
Probably, since its a different sensor with a different postprocessing. However, you wont see great jumps in image quality, which is more likely your question. Both cameras have a state of the art 24 Megapixel sensors. The details will be slightly different. For example the D750 has the weaker Anti-Aliasing Filter, so you will see a tiny bit more sharpness if you magnify to 100% on a computer screen, assuming you used a really good lens in the optimal way (no blurr from shaking, no blurr from subject movement, no blurr from lens brutally stopped down, etc), but that should be all.
I'm hoping someone has done this already.
I have thought about it, in fact I'm still thinking about it, but I think the difference between the two cameras is too small for me to justify spending a full 2k€ again.
But as I said - if I would get a new camera, I would definitely get the D750.
P.s.: I should maybe also mention the two problems I have with the D750, the reasons I decided to not get one in the end:
- Despite using the same AF sensor is still not as wide as for the D810 and D4s
- The shutter is louder than the shutter of the D600/D610
Both things are caused by the fact Nikon shrinked the D750. A change I would in principle welcome - but not at the cost of a smaller AF field and a louder shutter.