CGW, I have shot with this lens, I have used one a fair bit, but one day in the darkroom I had a friend over and we developed some film, his and mine, then did some prints.
We had attended the same event, motorcycle trials event actually, and a fair number of our frames were of near identical pictures.
What was noticeable was the contrast difference, the detail difference (resolution) and as you have already noted, flair from the odd shot taken into the light.
We did then put our cameras on tripods and looked through our respective viewfinders with our 100 and 105 Nikon and Nikkor lenses attached, you could see the difference in the viewfinder if you looked carefully.
There is nothing wrong with the 100 E Nikon lens, but it really isn't in the same league as the 105, especially the last 105 in Ai-S mount.
I also run a Sigma 18mm f/3.5, doing the same comparison as above on tripods with my friend's 18 f/3.5 with CRC (Close Range Correction) on his tripod, there was an immediate contrast difference apparent, as well as a slight lack of detail (resolution) in the Sigma.
Essentially one often pays for what one gets, whether the difference is worth it, is up to the individual.
In my case the 105 is my most important lens, so it had priority and I got what I believe is the best for my camera body. With the 18mm it is a low priority lens, so accordingly, I purchased a lower and therefore far cheaper lens.
Mick.