I just recently realized that "Dr. Noonian Soong" and "Khan Noonien Singh" sound familiar. Is there documented confirmation that the TNG writers were inspired by Star Trek II? Or is this purely a coincidence?
Directly - no.
They were both named after Kim Noonien Singh, who Gene Roddenberry knew during World War II.
Additional trivia from IMDB:
Roddenberry also had a tendency to reuse names - for example, Dylan Hunt was used several times.