I agree with Mobilexile. I wanted to buy the M8, I could afford it but was not sure I would like rangefinders, so I bought the RD1. Now I like that camera so much that there is no real reason to justify changing for a M8. Picture quality and new technology are not my main purchasing requirements. Yet, I would love to have a bigger LCD and more reactive interface, this is to me the biggest obsolete thing in the RD1.
For me, the RD1 is not an investment. I don't care if suddenly its value is divided by two, it is just a pleasure to shoot with.
Now if a RD2 would come around ...