To be more specific, I wear my Gallant Leggings +1, Shield Torque, and Buckler earring for recasting Utsu:Ichi when shadows are DOWN (it's a separate macro, not in my ichi cast macro). However, as a counter example, I would not swap in Koenig schaller (the 4 or 5 haste you can wear in that slot are too valuable for recast to give up).
When I'm recasting Ichi with a shadow left or when I'm casting Ni, I replace Dusk Boots (no Aurum yet) for Gallant+1 to lower the recast (unless I'm already at recast floor from double march+haste).
As others have said, if shadows are up for any significant amount of time, I basically try to maximize acc and haste. However, some things I tank, I'm recasting shadows or flashing about 90% of the time so I don't even bother with the acc gear macros - just haste or shield skill depending on whether I'm casting with shadows up or down. Sometimes there really is no such thing as "Idle" time.
I'd be willing to bet that there is a formula involved in shield block rate, and even probably a "soft cap", much as there is for other combat skills. However, no one has figured it out to my knowledge.