Since OP mentioned nebulae,
here is a list of all the real nebulae in the game. Out of these, the following have unique models of their own:
Barnard's Loop, Bow-tie, Bubble, Butterfly, Cat's Eye, Crab, Fine Ring, Flame, Hind, Horsehead (and cluster), LBN 623, Lemon Slice, Messier 78, NGC 6337 (now with an asteroid base), Orion, Pleiades, Ring, Veil Nebula West. (Veil Nebula East uses one of the generic models.)
Some might be unreachable depending on your jump range (and the Lemon Slice is unreachable for all), but these nebulae are sights you won't see anywhere else.
Oh, and you might want to visit some procedurally generated nebulae too. The nearest one, Traikaae AA-A h2, is just within your 5,000 ly distance, and although I believe its systems have been thoroughly explored by now, they can still offer some spectacular views. You see, proc. gen. nebulae can be in sectors with high enough star density that plenty of systems will be inside the nebula. In those, the nebula will cover the entire skybox, or most of it. Land on the night side of planets if you can, or just fly into their shadow if you can't, and enjoy the view.