Help me decide on a macro for my Fuji X-E1
Your information about those nearly antique Vivitar and Kiron macros is essentially correct. I owned the Vivitar Series 1 90mm f2.5 Macro for over over 25 years, used with Minolta film cameras, and it is the sharpest macro I have ever used, bar none, including my 55 f2.8 Micro Nikkor. At the time it was reviewed by now-defunct Modern Photography magazine, ca. 1980, its center lines/mm resolution was rated at 110+, exceeding the maximum resolving capacity of the chart, the sharpest macro ever tested. As you note, it was decidedly better than the 90 mm f2.8 Vivtar and it is no heavier than the 105 Kiron. Yes, you need the adaptor to go from 1:2 to 1:1 but I would consider using the lens without adaptor, if that bothers you, and cropping down - the lens is that good.
Fuji probably makes a prime macro too by now and, usually, I prefer original equipment to adaptations. However, I am not familiar with the current Fuji system.