To noticeably improve contrast on your HDMI connected Vive and monitors on an NVidia card, download a patcher called: NV_RGBFullRangeToggle.
This will restore the RGB ranges from 32 to 223 to the full 0 to 255 range, so this improves contrast a lot.
I figured this out by myself after wondering if my new GTX1080 would still need this patch (having used this before on my older cards), turns out it did, improving the contrast of my monitors. Then I wondered if the same would apply to the Vive, being connected by a HDMI connection, turns out it had fixed that as well.
Note that you need to execute the patch every time you upgrade your NVidia drivers.
Yeah, this only screws things up for me on my TV which is limited range.