LONDON (Reuters) - Investors who sent copper to a 17-month peak on hopes for a splurge of U.S. infrastructure spending by Donald Trump may end up underwhelmed given that the plans, even if successful, would add only modestly to world demand.  China dominates the global copper market, accounting for half of all demand, and an uptick in consumption there following further stimulus is much more relevant to the market. That, together with less mine supply than expected, would support slightly firmer prices, but not the wild frenzy that erupted after the U.S. election last week, investors and analysts said. “The infrastructure ambitions of Trump I think are meaningless in terms of the course and direction of commodities,” said Scottish hedge fund manager Hugh Hendry, founder and chief investment officer of Eclectica Asset Management, which has around $200 million under management.  Copper prices soared about 25 percent from the start of the month to a peak of $6,025 a ton last Friday, but have since retreated to $5,466 by Wednesday - still nearly a fifth higher since the start of 2016. Experts brush off the impact on copper of plans by the incoming U.S. president to spend $1 trillion over 10 years on building infrastructure, even as they are more upbeat on the plan’s impact on the U.S. steel sector. Unlike copper, steel prices are set regionally, and an infrastructure spending spree coupled with even stronger trade protectionism would initially be a big boost for the U.S. steel market, even though longer term the fear is that steel price inflation will cripple demand growth. Copper consumption in the United States has slid 40 percent over the past 15 years to 1.8 million tonnes last year, according to the U.S. Geological Survey.  That compares to 10 million in China, Thomson Reuters GFMS data shows. “Even an assumed 10 percent increase in infrastructure-related copper consumption would hardly matter on a global scale,” said analyst Carsten Menke at Julius Baer in Switzerland. “This is not least due to the fact that part of the increase in copper demand would be met by increasing recycling, considering that existing infrastructure would be replaced rather than expanded.” A position paper by Trump's advisors about his infrastructure plans (bit.ly/2eBQB1Y) published before the election did not mention specific projects, but referred to the broad sweep of possibilities including bridges, airports and digital superhighways. “Even if Trump’s infrastructure plan goes ahead, the impact on physical markets is likely to be only modest,” said Robin Bhar, head of metals research at Societe Generale. “If spending goes toward building roads and bridges, this wouldn’t be as beneficial for metals demand as extra spending on sectors such as power, transportation and capital infrastructure projects,” Bhar said in a note. More important is whether stronger demand in China on the back of stimulus earlier this year persists. China’s real estate sector is a prime driver of demand for industrial metals including copper, but investment has slowed and builders started fewer new homes year-on-year in September, the first such decline since December.  “These are lead indicators for copper demand by six to 12 months, but have clearly turned sharply negative,” Liberum analyst Richard Knights said in a note. Hendry, although dismissing the impact of infrastructure spending on commodities, says a wider fiscal stimulus could boost overall economic growth and give the sector a lift. “A trillion plus tax cuts are not (meaningless) and would certainly seem to be the first dramatic and politically supported step,” he told the Reuters Global Investment Outlook Summit. “That’s a world where commodities, you have to imagine, retain their outperformance.” 