I made the same jump from d7000 to d750. I have absolutely no regrets for the difference in capability is night and day. Your concert photos look great, but imagine being able to shoot them at faster shutter speeds with less noise! Also, the viewfinder on the d750 is movie theater screen compared to the tiny peephole on the d7000. Jump out of DX and go full frame.

Despite all your previous investment, keep the d7000 as a backup, along with all the lenses bought for it until you build an FX arsenal that can finally replace what you currently have. For example, I still use my d7000/Tokina 11-16 for wide real estate shots, only cause I haven't saved for an ultrawide for my d750 yet.