When it comes to 50mm Nikon has nothing at Leica quality. Zeiss makes some, but Nikon has just fell short. The f1.2 resolution is about as crappy as the f1.4 when we look at their speedier lenses. I am not sure on the f1.8 but the f2 resolution is probably on par with any Leica lens but it lacks the contrast so it will never compete in color.
I'm sorry to object but this statement is rubbish!
I've used all the Leica 50's both M and R at one time or another and sold most of them on here Noctilux excluded.
I've also used most of the Nikkor 50's and I can say without question that the 50mm F2 Ai is as good as any Leica 50 and Zeiss 50 for resolving, sharpness, colour and contrast.
I've recently been comparing one to my 50mm F2 R lenses (3 copies) and I can tell you the Nikon is sharper and has just as much contrast.
I agree with your 105mm verdict, easily as good as anything Leica has.
The 28mm F2.8 AIS is also in a class of it's own and I often compare it to shots from a 35 Asph I used to have.
The 35 Asph is a superb lens, no doubt but there are others out there. It all depends on what you want. I sold mine as I preferred the look of the v4.
The OP is happy with his lens and so he should be as it's a classic but there is loads of other glass available that will give it a good run.
The 'lacking' department for Nikon is 35mm lenses and once I used Leica I was always disappointed. I use a Summicron 35 on my Nikon's now and the gap in Nikon's line up is covered.