with some quick math with theorycraft addon:
spiritual healing 10% does not scale with +healing bonus's. it is just a flat 10% base amount added.
see below:
naked 0 spiritual -
ghealr1 933 - 1049
heal r1 324 - 372
naked 5 spiritual -
ghealr1 1023 - 1150 +90-101
heal r1 354 - 406 +30-34
current gear 0 spiritual -
ghealr1 - 1628 - 1743
heal r1 - 914 - 962
current gear 5 spiritual -
ghealr1 - 1717 - 1845 +89-102
heal r1 - 944 - 996 +30-34
+860 healing on gear unbuffed.
this means that mental strength WILL scale with gear and buffs as it is a flat 10% maximum mana modifier.
my unbuffed mana 6871 will go to 7558 (+687 mana)
my fully raid buffed mana of 9271 will go to 10198 (+927 mana)
Mental strength will scale with gear and extra +intelligence statistic, whereas Spiritual healing does not scale at all, nor does it affect +healing additives.
TLDR, get mental strength for more mana if you have enough +healing.
