Users have a lot of 'levels' to add tags and genres to - artist > release group > release > recording, and very few will add tags everywhere, a very repetitive task.

We can encourage people to add tags by suggesting tags from other levels (probably just 'higher' levels?)

An example mockup:

The above mockup shows the tag section in a release page. The tag suggestions are tags that exist in the release group, but not on this release, displayed at 50 opacity. It then takes only a single click to add them to the release.

I would also suggest that clicking 'minus' (putting the tag at -1 for the release) would hide them from this display.