There are many uncommon and unusual lenses that are not very good. There are lenses that did not go into full production because the alternatives were superior. The Elmarit cost much more than the 40/2 Summicron today, was originally meant as the economy version. So why pay more for the economy version. For photography, the Summicron is better than the Elmarit. For a collector, the Elmarit is more desirable because the Summicron is common.
The Elmar 35/3.5 lens on the Plastic Leica Mini is quite good, much better than the Nikkor 3.5cm F3.5 which is a coated copy of the Elmar that you mention. Some companies in Japan have fashioned a small industry around converting some of these lenses to Leica mount. From reading up on the Elmarit-C, the lens from the Mini is better. What you expect from pushing a Tessar formula lens to F2.8, ie the Elmarit-C. The Nikkor 35/2.8 found in the original Nikon AF cameras is another that gets converted to Leica mount. It is 5 elements, like an F2.8 Schneider Xenar. I have a Wollensak 35/2 in Contax mount. Maybe the only one, and it was worth all of the $20 of it.
The thread seems to be about one particular lens that is rare, asks about if it is a useful tool. I can generalize this to many rare and uncommon lenses that become "Ervin Myths". Who is this Ervin, and why does he spread these myths! (quote, D.W. from Arthur) I saw a Konica Hexanon-UC 28/1.8 that sold for $900 on Ebay! Another one for the list. Nice, but the Nikkor 28/2 is far better and ~$200.
So some useful advice for everyone- lenses that are desirable and priced for collectors are typically not worth the money for photography. That includes the 5cm F1.5 Simlar found on the Leotax. And the Konica 28/1.8. How did I get so many of these Ervin Myth lenses. Don't waste your money on one, unless you find it cheap.
KEH has a BGN grade 40/2.8 Elmarit-C for under $1500.
http://www.keh.com/camera/Leica-M-Fixed-Focal-Length-Lenses/1/sku-LM069991209430?r=FE
If anyone buys it, post pictures back here. What I'd like to find is a bad-glass Summicron-C 40/2. Use it to mount and RF couple a 40/3.5 Tessar from the $15 Rollei that I found.