If you are not going to actually use the camera – i.e. you don’t actually know how to use Shutter speed, Aperture, White Balance and ISO to get the shot you want, get whatever camera you like. If you aren’t shooting in manual or manual-assisted modes, they will all take nearly the same photos
You already have lenses from the greatest lens manufacturer on the planet and a legendary camera body. What Nikon lacks in first to market features is more than made up for in the quality of the optics, both optically and in mechanical quality. Canon only has marketshare due to their ability to get features to market well ahead of Nikon.
If you want interchangeable lenses, and a lighter body, get a cheaper one from Nikon and shoot that. There is nothing a new camera will do for you that the D90 will not. The D90 is one of the best cameras that Nikon ever made. Some of my favorite prints are shots I took with my D70, the D90 was them really perfecting the digital. Everything from the sensor to the UI is far better. The next generations are where they started chasing market with up and down scale models, sports specific shooting, etc. I can not say I mind, I am a landscape photographer and found the D800 to be the perfect variant for me. The D90 with an 18-200mm lens is a worthy travel set up. Throw in Nikons amazing 50mm F1.4D and you’re good for 99% of all you’ll encounter, day or night.
I frequently shoot my F5 and my D3 bodies, but the D800 is the most travelled, etc. The D3 really got put to pasture by the D800 but I like to shoot 2 bodies on some trips and its a great #2 if I am not going film.
My father just gifted me his FMNT, nice thing is I have all the lenses I’d ever want to use with it, if I decide to play with it. I likely will because it looks so cool.
The FMNT and a 50mm lens is about the size (and a lot heavier) than any of the new Sony/Fuji retro looking cameras… because it is they. While Sony/Fuji are all doing the mirrorless thing, they seem to want to behave like range finders, they look like those early film SLRs.
You are already in photographic nirvana, if what you want to do is use a camera.