Only we're talking about SCH here, not WHM; and I used Physick as the example for SCH, because it is the most potent healing spell they have; everything else on their toolbar are less potent than Physick and will benefit less from that 30 MND.
I haven't overlooked the Fairie benefits, but I can't really comment on them right now, as I haven't done extensive testing. I plan to pull some real numbers up on this tonight. You could look at Galvanize one of two ways; either you cast it once and hope it Crits or double cast it for a chance to override it. In normal situations you wouldn't do this, because it's a waste of MP, but theoretically if your MP pool were infinite; overriding your Galvanize would be the optimal way to heal.
This is the main reason behind my end of the discussion; if we had more PIE we would heal very differently and more effectively than we do now. Obviously 30 PIE isn't enough to tip the scales, but it's a step in the right direction.
If you check the screenshot back on the first page you can see I'm decked out in Allagan healing gear that I clearly didn't get in one run, so it's safe to assume I've healed at end-game at least a moderate amount. In truth I've been healing in the Binding Coil of Bahamut as a WHM and SCH for more than three months; though I don't see what this has to do with basic math.
You mentioned Twintania, so we'll talk about her then (since people love quoting Twintania mechanics to back-up a healing arguement, as though it's the only content there is); you haven't killed Twintania, have you? I know this, because you wouldn't be questioning the value of MP if you had. Unless you're one of the few that can clear Twintania without losing a single member (that would need raising) or without using Mage Ballad (that would reduce Bard DPS and waste MP better spent on something like Foe's Requium) we can assume that MP plays a vital role here.
I would also like to double stack my Adloquium for DS, but it isn't really viable in 13 minute encounter, for MP reason.
On another note; more PIE means higher ticks from Mage Ballad.
PIE is a main stat by the way, not secondary. You're about right on the 4-5 times better than any seconary stat though; Crit and DET are around 0.18-0.20 to every 1 MND. PIE however scales much better than MND does.
You're assuming healing smart and spaming heals are mutually exclusive, when you know that Galvanize overrides itself. I'm not in the habit of doing this though, because I could be waiting ages to pop a Crit on Adloquium, but if I had the MP I would do this; and so would you.
Let's not forget that the OP is talking about playing both SMN and SCH here, so regardless of what you say; MND is entirely useless to SMN and INT is entirely useless to SCH; VIT and PIE are not.
Sorry if I missed someone out, it's hard work quoting this many people! As for the OP, I'd go with whatever you think is best, given this information. It's a simple matter of taste and non of these attributes will be sorely missed. If it wasn't for the HP problems, most good healers could heal any end-game content in their bikini; stats mean very little to a healer in comparison to their DPS and tank counterparts.