One reason for declining manufacturing costs in China is that it is shifting more of its production to robots, counterbalancing the effects of rising wages. In a report to be released later this month, the International Federation of Robotics found that China accounted for 25 percent of industrial robot sales in the world in 2014 and had purchased about 56,000 units, with the automotive industry the leading buyer. China's share of the world's robots is up from last year's 20 percent, which made China the country with the largest percentage of the world's industrial robots.
That said, it may take a while before many U.S. manufacturers ramp up their production in China significantly. For one thing, many manufacturers in China aren't likely to dangle price breaks to U.S. firms easily, even when declining overhead justifies it, according to Gary Young, president of Avela, which has helped companies source products and services in China since 2002 and has offices in Houston and Shanghai. Often, he has found, U.S. firms find there is resistance when they try to renegotiate deals with Chinese manufacturers whose costs are declining.
Read MoreHow one US manufacturer is buffering against China
"There's always pushback," said Young. "For the most part, manufacturers' profit margins are pretty small. They are anywhere from 4 percent to 12 percent. That's all the profit margin they have. They guard that. That's their lifeblood."
He added, "Everything is a negotiation. It can take a couple of days. They try to wear you down. Their attitude is, 'You're an American. You're rich. You really shouldn't even be doing this.'"
Certainly, even with the potential for lower costs, not every manufacturer wants to make products in China. "There is supply-chain risk," said Greg Cullison, a senior executive at Big Sky Associates, an operations management advisory firm in Charlotte, North Carolina, and Washington, D.C., and an expert in geopolitical risk analysis. "China is very far away. You have to consider the shipment costs. Are you going to be subject to export tariffs or delays, which are actually costly in shipping the goods?"