Partial vacuum and whole table vacuum
I don't think that you can tell from the "verbose" listing whether any pages were skipped because they were known to contain only visible tuples.

I think that it will only vacuum pages flagged as "all visible" if it decides to freeze tuples in the table, either because of approaching transaction wraparound or because you explicitly ran VACUUM with the FREEZE option.  (If you use the vacuumdb command-line executable, this is the -F option.)

In our shop we supplement the autovacuum activity with a scheduled VACUUM FREEZE ANALYZE on the database during non-peak hours.  That minimizes the overhead of autovacuum during peak hours, and slightly improves query performance, because visibility checks are simpler.