As taric you have 2 things in mind. Keeping up with the carry and keeping everyone alive While stunning. The spirit visage helps to do just that. Since you get healed for healing allies, i do not see a reason to not heal someone when you have the spirit visage do to you having magic resist, health regen, and heal for 20% more. on a 100 heal thats 20 more for yourself just for being supportive. The soul shroud gives your allies cooldown reduction and mana regen which they will love you for, and health which you could use yourself. Abyssal's = useful for the MR and Magic Pen. Now that you have the support get a sheen and make a lichbane to keep up with those fast carries, as well as deal a little damage of your own.

By the way the reason you don't get radience until level 10-11 is that at level 6 you do not have the mana regen to leave this on, and at level 2 it is more worth while as it is for team fights and end game which start around lvl 10-11 anyways.

Pros:
2 second stun at level 1, with ap health and mana regen
Team CD reduction mana and more health for yourself
Slowing shatter, excellent farmer due to ap for shatter
Late game damage and support

Cons:
Not as tank as one would like
Mana regen is kind of low
Hard to get time to farm when supporting

GLHF