I have to agree with dreams. The only "mastery" that really has any benefit when not in a party is discord. All the others could be of some benefit to a non-standard template, but that is about it.
I use peace mastery to regen stamina while running through abyss (when dragging my GD along), but that is about all I get out of it. I tried to use it to beef up a discord tamer's mana regen, but the +8 hardly put a dent in their upkeep.
I am echo cervesa's opinion, better to use mana for cast and heal and general support. (shameless plug, that's what my script is all about).
Plus, if you are set up to regen mana for bard masteries, you can actually do more damage over time with mindblast. As I remember, over time, discord equates to about the same damage as lightning bolt.
One thing I have not seen mentioned is lich form. Wraith form would help more, but the 100 SS could be a tight fit.