Mr. MacLellan said that any negative effects of the legislation’s abolition of the so-called 1031 like-kind exchanges for art — which allowed investors to avoid capital gains taxes when they sold a work by replacing it with one of similar value — would be more than outweighed by tax savings spread more widely in the upper reaches of the market.

A New York Times analysis of the new tax code identifies corporations, multimillionaires and private equity financiers among those who will benefit most. Wendy Cromwell, an art adviser in New York, sees such groups as “the exact demographic” of collectors at the top end of the market.

“But art is in a funny place,” she added. “Art has become defined by what happens at the top of the market, and I don’t see that market changing in the coming year. I do see the middle market being further eroded.”

From Ms. Cromwell’s perspective, the untold story is the silent majority of less-wealthy collectors who own works by midcareer artists whose auction values are now lower than their original gallery prices. “It’s demotivating people from continuing to buy,” she said.

Another factor is that millions of middle-class Americans are likely to see their taxes go up under the new tax code, even if they see a tax cut next year. Collectors from this stratum of society traditionally formed the hidden bedrock of the art and antiques trade. But most have less money to spend, a point reflected in the way lower-value sales have changed at the international auction houses.

The “affordable” price range of $5,000 to $50,000 is no longer the province of live auctions of antique furniture and collectibles for the middle-class home. Instead, it is increasingly giving way to sales of luxury accessories, including jewelry, watches and handbags, in a mix of live sales and online auctions around the world.