A hobby is just that and an investment is not the same. Expect the ROI to be the enjoyment you receive in using the camera and don't worry about if it will appreciate in value. You can be disappointed in both if you try to mix them together. If the equipment used in your hobby happens to appreciate over the long term or depreciate as fast as other equipment, be happy but, do not plan on it. If buying a Leica for use, get a serviced user and concentrate on the glass. If buying as an investment get the best affordable and put it under glass.
Some years ago I bought my Leica and have loved using it. Today it is selling for about the same price as I bought mine for. My profit has been the enjoyment in using a camera I felt good with.