Found lots of these places by word of mouth, internet, contemporary news, preservation organizations, and reading historical documents. Yup there have been countless places where it just wasn't worth pulling out the camera.
This artwork is located in Pennsylvania, and has no relation to Germany or the Nazi party as far as I know.
The eugenics movement in PA was only carried out at the Elwyn Institute, where 270 residents were sterilized. No sterilizations took place at Pennhurst, and I don't think U.S. eugenics at institutions were based on racism. http://www.uvm.edu/~lk.../eugenics/PA/PA.html
Patients stricken with TB had to remain isolated within the hospital complex for months or even years to prevent spreading the disease, creating a kind of institutional lifestyle. Entertainment was an important way to relieve these stresses of being "cooped-up" too long, so movies, plays, music, and games were circulated well throughout the hospital (remember too that television was still in infancy when these buildings were constructed).
The same thinking applies to the old psychiatric hospitals, although focus might lean more on the therapeutic values of entertainment.
There are some seemingly valid stories in the comments here; I've found it difficult to find much history about Letchworth online as well.
I think your best bet might be the town historian, although you might need to check three places - Haverstraw, Theills, and Stony Point as the hospital campus is located in all three municipalities.
The development of the antibiotic Streptomycin in 1946 was the beginning of the end, I think it had mostly died out by the early 1970s. Drug resistant strains of TB have started to re-emerge in the 1980s though...
The power plants were built specifically for the hospital as most institutions were situated in remote areas where they could not connect to a city's steam and power lines. Coal was brought in by locomotive and burned to generate enough power and steam (for heat) to supply these massive hospital campuses.
This power plant at Kings Park is actually the fourth plant built over the lifetime of the hospital.