I was at both Las Vegas auctions this year to meet with collectors, not to buy. I was a guest of the Barber museum and, because of their long experience in buying at auction, benefitted greatly from extensive discussions with them about the nature of both auctions, as well as benefitted greatly from long-time buyers I also met with. However, if anyone has issues with any of the following observations, they are entirely my own (mis)interpretations of what I learned from these discussions and my own observations.
The fact that three Black Shadows sold at Mecums for $99k and another sold at Bonhams for $97.8k seems to indicate a current price of ~100k. However, upsetting this simple valuation is another sold at Mecums for $143k. I didn't inspect any of the Vincents from closer than a few feet, but based on the catalog information -- which is a very problematic way of assessing any machine auctioned in Las Vegas -- the $143k bike had been independently judged at a show to be a "100 point" restoration, whereas the others either have stainless and chrome where they should have had Al and cadmium, or where deviations from 100% original aren't noted in the catalog. If any conclusion can be drawn from this it's that buyers will pay a high price for a "perfect" example of a Vincent, but considerably less for one that might be every bit as functional (or even more functional), but that has non-stock parts on it.
Misinformation is worse than no information. Words like "concours," "perfect restoration," "100% original," "very correct," etc. printed in an auction catalog mean nothing. Anyone bidding by telephone based only on a catalog description is, well, worse off than had they not read the catalog.
Another observation that can't be mine alone is that all money for any bike being sold at Las Vegas should go into the external cosmetics. Money spent on anything not visible to the naked eye, such as rebuilding the engine, gearbox, brakes, etc., is wasted. No amount of time spent applying over-glossy paint or over-polishing alloy is time wasted.
Bikes hyped on social media prior to the auction will receive considerably higher bids. Ideally, to generate exceptionally high bids, the owner and bike will have appeared in a reality TV program. Because the late "Indian Larry" appeared on the show 'Biker Build-Off' ~15 years ago he has been mythologized by a certain segment of the population. As a result, although the choppers he built are rather ordinary (which is heretical for me to write...), two of them sold for ~$200k ea.
Numbers? We don't need no stinkin' numbers. Although in general matching numbers machines sell for considerably more, it appears plenty of attendees bid without having done their homework. One cosmetically-beautiful 1959 BSA sold for top dollar despite having a 1957 engine in it, which a bidder would only know if they had checked the numbers. I expect that had all the bidders for this bike done their homework it would have sold for $15k rather than $27.5k. As far as Las Vegas auctions go, Cavet Emptor is a gross understatement.
Despite the above, there are bargains to be had. The first bike to be sold at Bonhams was a pretty 1972 100cc Yamaha that went for only $575 including the buyer's premium. Who among us doesn't have a child (or grandchild or, er, great-grandchild) who couldn't make use of such a machine for their introduction to motorcycling? And for only $575. You would have to pay 5x that much for the least expensive new motorcycle. Two bitza Gold Star that appeared to be in good, rideable condition sold at Mecums for $7.7k and $9.9k, which would put someone on the road at less than half the price of a "proper" Gold Star.