Sure the 'proof of originality' is one of the facets of this topic, but especially if we think about vintage Heuers I think they bring an intrinsical added value. After all especially the boxes seem to have become cult items by themselves, and people (though personally not me) seem to be willing to pay even large sums for them alone.

I would tend to agree with Jeff's opinion that the overall value increase may be in the 40% to 50% if wholly matching, somewhat less (towards Sam's estimate) if they just are original but not altogether fitting. Also, extras themselves vary a lot both in their availability and the value they add: as far as I know, Heuer hang tags seem to be even scarcer than boxes and surely than papers but they seem to attract less value despite IMO they are better proofs of originality and 'good ownership' (as it were) than papers...

Cheers.

Fabrizio