Tony: I appreciate your quandary... it's one I shall face in the future. I have a stable of Olympus OM equipment. I have started my daughter off with an OM-2/50mm f1.8 as a basic kit, based partially on the fact that I can give her surplus or duplicate lenses and accessories, and am very informed on the OM's use, etc. Granted, the OMs are more like your Centon/Pentax combo than a Nikon F100... I hate LCD screens, menus, etc.
But I have fallen in love with RFs, both fixed lens and interchangeable. I don't have any of the latter ... used to own Leica M3, but am now longing for the new Ziess and Zeiss M mount lenses.
Since the Chief Domestic Officer would be quite unhappy if I did not unload some equipment before going on a buying spree, I am contemplating having to sell some OM gear (which I've owned since the mid-70s when the OM-1 was new to the scene) and concentrate on RFs and my 4x5. Aaaargh.
You don't seem to have such constraints nor emotional attachment to the Nikon. If it were me I would sell because then you would not even have it to fall back on, thus perhaps "forcing" the use of the other cameras which seem to be driving your creativity.