1. I think that it would helpful to first put the sentence in "regular" order:
The FINDINGS that playing sadistic computer games may increase aggressiveness + ARE + of more concern.
a. I believe that most books would explain it this way:
i. "of more concern" is a prepositional phrase that is acting as a subjective complement.
That is, "of more concern" refers to the subject "findings." ("The findings + are + of more concern.")
***** Here are some examples from one of my books:
a. My watch is of solid gold. ("Of solid gold" refers to "(my) watch.")
b. He thinks this book to be of great value. ("Of great value" refers to "(this) book.")