Healing is relative to how much DPS your group is outputting and how much appropriate cooldowns both the tank and healers are using. This is why "trialing" healers is one of the most difficult things to do when looking for one in progression statics. That being said, here are simple rules for DPS gains via spread vs. fights.
Enrage limits the amount of GCDs you can do per fight, thus one can assume Balance/Arrow would be best for those fights; however, you must factor time & resources into it. Resources such as TP/MP restrict the spamming of the highest potency GCD skill, and so do skill conditions (positionals, chain skills, etc.). So in fights that have a relatively short enrage time, i.e. Faust, Balance & Arrow > Spear. In fights with long enrage, Spear becomes more efficient as it saves your more time vs. Balance. Expanded Balance is now 30 seconds, but prior to this patch it was 15 ~ 20 seconds (with Celestial Opposition). 5% damage buff essentially means it takes 20 of the same skill to make up 1 free skill, which is equivalent to over 40 seconds spent to gain one extra GCD. Spear decreases CDs by either 10% to 20% when used, and makes coordinating with this skill super-fantastic. Shaving off over 10+ seconds off Raging Strikes, B4B and alike makes the skill really great, it just requires a lot of coordination. No coordination makes the skill very limited.
Healing wise, treat Essential Dignity like a Benediction but use it like a Tetragrammaton. What this means is that since it's our only instant-heal skill, don't use it on the fly. Only use it if you need to catch up in healing or if you are 100% sure that you are not going to need it within the next 40 seconds. Reason being is because since it's our only instant-heal it is the only way to catch up on healing. GCD healing is restrictive in interval type healing which is akin to regens; however, you have more control as you get more burst heal per GCD vs. heal per HoT tick. In addition to this, Essential Dignity is around 650 potency at 60 ~ 65% and at i193 it heals for around 6700 ~ 6800 HP (1k Potency) at 1 HP.
Figure out what to use Synastry. Finding situations where you'll most benefit Synastry is the best. In AS1, like many have said, Synastry's CD aligns with double preys. Throw it on tank and coordinate with your healer duo. How my healer partner and I set up double prey conditions was if prey is ever on me, my Scholar would heal me and I would heal the other target. If they were on our respective tanks, we'd heal our own tanks (and I'd throw Synastry on other tank or other prey target). If they were on DPS, I'd call it out
As for suggestions Dyvid... The essay is coming along, but the current "buffs" are more of a bandage patch that fixes performance rather than class vs. class. The issue of balancing comes with our watered down healing kit of both SCH & WHM which trades off vasts amount of healing and defensive utility (Emergency Tactics, Fairy, Benediction, Cure III, Crit Adlo-effect, Indomitability, Assize, Fey Illumination, Whispering Dawn, etc.) for cards which are buffs that are nice to have but not necessary. Buffing both healing amounts and card effects to provide impact that the group can feel in terms of DPS would make AST > WHM/SCH when it should be AST = SCH = WHM in terms of viability. What they should do is add in its own way of healing to define its class, because at this moment they're essentially consistent but weaker version of SCH & WHM, but provide card buffs.
Where a White Mage provides raw healing a Scholar provides shielding.
Where those healers provide their defined healing, an Astrologian mimics a SCH & WHM and has cards. That's not a good design in my opinion, especially since cards aren't tied to their core which is... Y'know, GCD... Something that makes up practically almost all your actions in the fight.