Dale, the tiny (mm or so think) and light (think grams) LTM–Leica M adapter should give you no cause for any concern; my CV 12/5.6 uses one and once it's screwed on, you'll forget about it. And I have not found that using this mount affects saleability for me. The tiny adapter can be marked to bing up Leica framelines too, as I understand it.
Interestingly today, my version of the 12/5.6 is more expensive than the M-mount version, but the reverse is true for the 15.
Anyhow, on reflection, I am finding these days that ergonomic considerations are tending to trump all others for me, now that IQ is simply good enough for the things I do. Using the X-E1 around the house this last week with the pancake and a number of OM and CV lenses has been so much fun and I love both the feeling of the camera in the hand, and the sheer brilliance of the MF aids (as mentioned, I use focus peaking combined with focus magnification).