The 4 piece bonus is very nice when you have the opportunity to stand and cast, and aren't being hit. I suppose the trick is to create situations where this is true. One big problem I had was noticing when the bonus procced. I wanted a noise like the clearcasting proc and after looking around for a while I couldn't find exactly what I wanted. So I wrote a very simple addon to do it for me, and it's been working very well.
I created these three files:
if arg2 == "SPELL_AURA_APPLIED" then
if arg6 == UnitGUID("player") and arg10 == "Nature's Grace" then
elseif arg6 == UnitGUID("player") and arg10 == "Wrath of Elune" then