I've read a bit about cases where even if you renounce your US citizenship to the foreign government to become a new nationality, you can still tell the US Govt 'I was just kidding to those foreigners', and you're fine. It's only really an issue if you renounce it to the US Govt directly.
Yes I've also heard about people 'renouncing' their American nationality to foreign governments, not informing the US, keeping their passport, and not having any issues. I've also heard about people exaggerating facts to ensure their children (born abroad) obtain US citizenship (possible if the parents are American and have lived in the US for some amount of years - there's the catch).
The problem is that you really don't want to be in a limbo state with your citizenship. Some politicians or bureaucrats in the future could decide that there are a lot of people abroad collecting social security, let's audit their citizenship.
