This is just my humble observation.
From the time the new M Type 240 was announced up to now, there were and still are a lot of talk about how it might be better or worse that the old M9. There seems to be 2 camps here, one that is somewhat unhappy with the new M for variety of reason from newer technology in the new M that cause the IQ to look more digital or the fact that it is bigger or heavier. The other camp are the early adopter that just needs to have the latest and the greatest. I see the similarity in auto enthusiast. Whenever BMW introduce a new 3 series, there will be 2 camps, one that are the early adopter who think the latest car is the best, and the other are (not sure if it is the right term) purist who swore that the new car is never as good as its predecessor, it is heavier, doesn't handle as well, too big, ugly design etc.
The early adopter will always be the early adopter. They have the money (or will come up with the money somehow) to get the latest and the greatest and love it. Some of the early adopter are also the people with a lot of financial means. They see the product as a status symbol to say they have it and the rest of you just can't afford it. Again, Leica, like BMW knows that well and I think really caters to this group. Just look at the number of limited edition this and that. Not all early adopter are rich or seeking status symbol. Some just love or need the latest technology for work or needed the features that is not available in the earlier model.
As for other camp, at the end of the life-cycle of the product, most of the people who did not like the product when it was introduced now can't say enough good things about the product. They also start comparing the soon to be released product with the current, about to go away, product and would swear that the old product is better than the soon to be released. I see this somewhat with the Leica Ms and the same with BMW 3 series. This only happen to products where you have very enthusiastic followers. These are also great products to begin with and have set the bar so high. The product usually have a very long product life, long after it is discontinued.
Edit: As Jono pointed out below, there is also the group that are true users of the product. These are people that will use all the different version of the product and are serious about their craft whether it be driving or photography. The see the product as a tool and might find features in the new product that is not available in the older version.