Racing pedigree will play a part for sure. Just as LeMond makes some Gitanes more popular Armstrong will make the then older Trek Madones popular as well.

Seems like you all are leaving out an obvious choice: There will probably always be a market for lugged steel as mentioned above and combine that with racing pedigree you have as close to a sure winner as possible, IMO. Therefore I think Eddy Merckx in either current "vintage" models or the more recently re-introduced Molteni replicas will always find a home.

Of course there will be a time when it will be impossible to get a new Sachs regardless of your patience; impossible to say if they'll be a collectors niche or not.