"Everyone is thinking more European than before," SPD parliamentary deputy chairman Axel Schäfer said. "There have not been such tight bonds between Germany and France since the times of Willy Brandt. We have so many meetings, campaign appearances and agreements."
Schäfer's party is currently trying to steal a march on Chancellor Angela Merkel by presenting itself as the natural ally to the new French president Francois Hollande - and work on joint policies for supranational issues such as European debt.
"The cooperation between the SPD and the French Socialists has never been so close," he said.
The German described Hollande as a sympathetic antidote to his defeated opponent Nicolas Sarkozy - a close ally of Merkel in recent years. Hollande is currently trying to coordinate a more left-wing response to the European debt crisis, by resisting the drastic budget cuts proposed by Merkel and his predecessor Sarkozy.
One of Hollande's more radical measures is an increase in France's top rate of income tax to 75 percent, while he has also reduced the retirement age for some French workers to 60.
But the SPD is apparently not planning to copy his tax idea if it gets into power in the autumn 2013 election. Schäfer said taxing the rich was the right way to go, "but our top rate of tax should stay at 49 percent - that is also psychologically right."
The SPD has been gaining ground in recent German opinion polls. The latest weekly political trend survey, conducted by state broadcaster ARD, put the centre-left party two percentage points up from last month at 30 percent, and just four behind Merkel's Christian Democratic Union.
The SPD's worry though is the continuing decline of its coalition partner of choice - the Green Party, who dropped another point to 13 percent in that poll.
The SPD is also hoping to leech a few stray centrists from the more hardline Left party, which dropped to its lowest poll ratings since 2005 this week.
Earlier this week, SPD General Secretary Andrea Nahles provocatively invited any disgruntled Left party politicians to join her party. "They're all welcome," said in an ARD TV interview on Tuesday.
The Left party is currently riven by internal divisions after last weekend's party conference, where new leaders were elected after a drawn-out leadership battle.