What would happen if those gravitational waves were much stronger? What if those gravitational waves detected would be actually so strong that the distance of those mirrors moved would be larger? Not 1/1000th of proton but rather one millimeter, or one meter or even more? What would happen to us? How big would these black holes had to be and how much energy would be released in such a process?
Based on a post by an Astrophysicist my understanding is as follows:


Gravitational waves would still be faint to detect irrespective of the size of the Black Holes. BTW aren't black holes meant to be more concentrated rather than bloated?
The distance from ground zero is what matters rather than the size of the colliding black holes and even if they were a billion times closer they would still not measure up to 1 mm.


There wouldn't be significant impact from the waves themselves rather the Black Holes are the ones that would do the damage.
For the shift to be 1 mm we would require a force enormously stronger than that of a gravitational wave.  



Here's the link to the article: http://www.forbes.com/sites/briankoberlein/2016/02/13/could-gravitational-waves-ever-be-strong-enough-to-feel/#1605e7fa4aac 

Disclaimer: All my points are a result of my learning from the above link rather than any native knowledge or original research that I profess to have done.