Some thoughts regarding the Zodiac Ring, obtained from the WoTG Windurst-S path "At Journey's End" quest--
Thus far, the ring has been demonstrated to offer 3% damage bonus on matching day & spell element, and removal of damage penalty from mis-matching day & inferior spell element. However, one open question remains whether or not the ring has any impact on magical accuracy (very difficult to test).
If there happens to be an penalty negation for M.Acc as well, this ring could be a useful swap piece for enfeebling. Paralyze on Firesday, Sleep on Lightsday, etc?