Not to go back and beat a dead horse but one thing I did notice on Spirit....
It needs a 4os shield and the only ones that exist are the Monarch and the Ward....
The monarch (the lighter shield) still has a level req of 54 and an str req of a whopping 156. So I suppose it depends on how much vitality you want to sacrifice and how it can affect you choose items that give you the str needed to equip this thing for what might not be a substantial improvement over what you use now....
Even using an Enigma your str will only be increased by about 63 or so give or take depending on level. If you combine this with an anni charm to give you say an additional 18 or so if you have a decent statted one....you're still going to need to sink about 59-60 (varies depending on actual stats of gear) points into Str or use charms that take up space to equip the darn thing (which would reduce vitality or resists or skills anyway).
Considering this is supposedly a caster shield......is it worth it? I don't know.