Currently when I go to "Auto-tag by Album" or track, the genre pulled from the internet is almost always something more generic than what I'm looking for. Almost everything I have comes up as "Rock." The best system I've found yet for getting a more specific genre is the autotagger script for mediamonkey that pulls genre information for the top x (configurable) hits from last.fm. Polvo, for example, comes up as "Rock" on musicbee and "Math Rock" on mediamonkey. Minor Threat = "Rock" on musicbee, "Hardcore" on mediamonkey. This works very well but last.fm has a number of non-useful tags in the top slots as well (female vocalists, for example, which is hardly a genre), so it has a configurable blacklist and whitelist.
On another thread you said genre already comes from discogs and last.fm as well but I don't see any way to access any varying genre info.