To expand on art in the game, players should be able to dismount art from walls and turn them into items; so they can be traded, moved or what have you. Further on that, paintings should be invincible but easy to take down; as long as you have access to build in an area you can take them down. That way art is not destroyed and can be stolen plus people can’t troll with it. OR after destroying it, it becomes a lootable item.
Guitar has a glitch, if you play a note and scroll your mouse wheel at the same time or right after, the sound is prolonged and distorted.
As for music, is it possible to maybe add .abc files? http://www.lotro-abc.com/ Starbound makes use of this and has many instruments. Players can get into groups and play whole songs as a band.
Both of these additions would further improve the games social dynamic. Players will march around as bands or choose to paint for others. People will have art museums and others will try and raid those masterpieces.