American investors are important but not irreplaceable.
The Germans should woo other investors, from different parts of the world, who take a longer-term view and value engineering prowess, thoroughness and quality above all else. Each offering to selected inward investors should be tailored to those preferences.
Personally, I would look outside of Europe to places like Singapore, whose inward investment vehicle is Temasek, to countries like Kuwait, Saudi Arabia, Qatar and even parts of India and China.
The UK is good as Dr Alf knows, at getting foreign investors as individuals to invest here but less good at attracting money from Sovereign Wealth Funds.
Germany could analyse what the UK does and re-engineer the process built to its own strengths. It should then do the same exercise with countries it would like to get inward investment from, and see where it has strengths which compliment the weaknesses of the target inward investing nation.
Out of that discussions can emerge.