A wise country or area would forget about global anything and strive toward self-sufficiency, with no debt to global interests and no need to buy or sell anything from other countries.
The US was great once. That's when we were self-sufficient and exports were just icing on the cake. When immigrants were people who were allowed to enter the US to fill jobs that US citizens couldn't. When a future for someone who prepared and was a good employee was pretty much assured.
Greece and some of the now-impoverished countries in the EU were doing just fine, with vibrant cultures and economies, until their leaders sold out to the EU masters.
If Greece can break loose from the EU noose, good for them. In the US, if any state can break loose from the feds, go for it!
JMHO
With the US, it was when the liberals started taking over and implementing their social programs and their tax increases. Does not help having the highest corporate tax rate on the planet, never mind refusing to allow vital industries to expand (e.g. oil refining). The list is far longer than that.
Since Greece seems to be tending to vote far left, they sure will not tend towards leaving the EU empire.