Just my thoughts. The message I am trying to communicate is if you really want to protect the value of your bike then simply invest in art/equity/bonds whatever. There isnt much you can do to protect the re-sale value of the bike. Its a toy that can put a big smile on your face, nothing more.
Hey, not just your thought. But it is common sense, if you are buying a new bike you will lose money no matter what.
HOWEVER, if you buy a privately owned used bike, chances are you might hit a good deal and be able to sell at a greater value in the future. THAT's an investment. But it would depend a lot of factors. I know friends that have bought and sold bikes for higher value, at least 2 of them.