Ralf:
I agree that this was a great looking chronograph, and that this is a very rare piece. Still, the Blue / White Automatic is the "signature" version, and I believe that these will always fetch the top price, compared with the other Monacos.
In my experience, scarcity does not always tanslate into value. There was one Oriosa watch that I looked for on ebay, every day for two years. When it finally appeared, it was mine for $110 (and probably worth about half that price).
While some collectors want to own every version, and would have "needed" to buy this one to add to the collection, other than that, I believe the highest prices will be for the Blue / White Automatics. Some people will still look at the 7740 and say, " . . . but it's not the one Steve wore in le Mans." I believe that the value arises from this history / association, and that the 7740 is often thought of as being something other than the "real thing".
Jeff