Definitely the Siffert, with all the motor racing connections it carries along, will be one of the strongest gainers in the general appreciation.

How much it is going to rise, comparatively with either other Autavias or generally other Heuers, is highly debatable, but IMO the price range Abel suggests is a very sensible one given overall market conditions.
It has to be said that this very watch seems to have a special appeal also for those, like me, who are not real Autavia nuts: I don't own any Autavias (regrettably...), but should I have the luck of choosing one just for its style, regardless of price, it'd be definitely this one, in any of its various incarnations of hour counter and hands.
Cheers.
Fabrizio