I think the impetus of this thread is multiple posts on Photrio that purchasing a Leica is an investment in that you can get your money back when you resell it if you don't like it. Honestly, that applies to just about any used camera these days that is bought at a reasonable price.
That at its best is a theoretical consideration.
If one got a lot of cameras and has to get rid of them in short time (as in moving into smaller space), these cameras actually would cost money for waste haulage.
Easy to sell are typically only a few 3-digit collectors models. I have seen huge collections where the commercial buyer only paid for these few and took the rest only to dump it in some way or the other..