Johan, the UC-Hex is not much more contrasty than the W-Nikkor, you have already.
Actually, it surprised me, how so very contrasty the W-Nikkor is for an early 50's lens!
All other Japanese fast LTM 35mm, I have tried, have either much lower contrast, as the W-Nikkor or have much less resolution than the W-Nikkor (this is actually the major strength of the W-Nikkor - resolution!).
The only lens, I can think of in LTM mount, that would be an upgrade for you in resolution (apart from the LTM Voigtlander lenses, which I didn't have), is the UC-Hex.
I use my UC-Hex a lot, whereas the W-Nikkor moved into dry storage almost permanently (as the UC-Hex is so nice).
The problem with your situation is, that you would likely have a straight trade from one very nice, rare lens to a more modern, not as rare lens.
Are you willing to let go of the Nikkor? I wouldn't do that.
There is a medicine for your issue, if you use Lightroom - create a development profile for your W-Nikkor shots, that helps the contrast.
Always use a lens hood and when shooting B/W, use filters to alter contrast.
I wouldn't pay any money on a limited edition LTM 35/2 Summicron (mostly, because I don't like that lens' rendering anymore, compared to the beautiful W-Nikkor/ UC-Hex rendering).