Recube my Shield

Currently my shield's potential is sitting at 12% M.Att, 20% Boss, 9% M.Att, and I love how much it shoots my range up because it makes my DoT go way up too, but I don't know of it's worth keeping or if I should aim for say 60%+ ish Boss. I easily have enough NX saved that it shouldn't be a problem to land that, but if I do it I know it'll be near impossible to land those lines again if I end up regretting it.
I have around 850 M.Att from equips alone, 177% Boss, and 97% Ignore if that gives you any idea.
I guess it's a pretty obvious choice, but I just need a little more convincing because I'm really going to miss that massive range increase.