> Unless they release actual regulation I don't believe their opinion on how to interpret existing regulation really matters, or am I missing something?
To us their opinion only matters insofar that they are experts on the matter, but I don't think you are really missing anything. Courts are free to decide otherwise.
I believe the US copyright office's opinions are based on precedent set in court and on their own expert understanding of the relevant laws, so you should not read that as them setting policy, but rather as them explaining and summarizing.
However note that the copyright office runs a small claims tribunal for disputes under $30k. If one chooses to make use of that, their opinion do start to matter a bit more.