I'm sorry if this question has been asked a thousand times before, but perhaps my question is a bit different. At least I hope so.
The only prime lens I have between 28/1.4D and 85/1.4D is currently the 50/1.8D and sometimes the "gap" feels a bit too wide. I do have the 17-35/2.8D and 28-70/2.8D zooms, but they don't cut all the requirements either:
* nice bokeh
* aperture ring
* macro
* reversability
Is there a 50 mm lens that offers all of these, or should I get two (or more?) lenses instead?
Have you considered a 60mm f/2.8D?
The biggest challenge with a 50mm lens is the "nice bokeh" part. For a while, I owned both a 50mm f/1.8D and a "long nose" 50mm f/1.8 AI. The only difference I could see in the optics was in the coatings -- bokeh is best described as "indifferent" with both lenses. While the older 50mm f/2 used a slightly different optical formula, I don't remember it being any better. Any of the manual focus lenses will offer better focus feel, but beyond that I doubt you'll see much difference from your current 50mm f/1.8D.
It's been so long since I used a 55mm micro I can't tell you anything about the bokeh, but I don't remember anyone praising it for that "back in the day." As Bjørn mentions, the faster 50mm Nikkors aren't the best candidates for close-up work due to aberration and field curvature concerns.
The 60mm f/2.8D has an aperture ring. It can be reversed using a 62mm->52mm "step-down" adapter ring, but since it's a native 1:1 lens doing so is mainly useful on a bellows. I'd rate the bokeh as "fair-to-good," which IMO is a solid step above the 50mm f/1.8D. I purchased a copy in EX condition for under $200, although $225-$250 seems to be more of the norm.
Another "black-tie" alternative is the Zeiss Makro-Planar f/2. Compared to the 60mm f/2.8D, it's a stop faster, has significantly better bokeh, and has far better focus feel. On the downside, it's a manual focus lens, only goes to 1:2 without additional accessories, and costs about three times as much in the same condition. It also requires 67mm accessories, so I'm not sure how well it will reverse.
One of my planned "snow day" activities is to compare three (reversed) lenses on a bellows -- the 50mm f/1.8 AI and 60mm f/2.8D I mentioned above plus a Rodagon 50mm f/2.8 APO enlarging lens. If there's interest, I'll post the results here.