finding an elemental shard would always be of benefit rather than hit-or-miss.
For a mod, I'd get rid of the Shards or wait for an option developed by Stardock that allows spells to have more than one cost, so we can choose when casting, which price we want to pay for the casting.
I actually have! Check out my mod to take a look at specifics and make suggestions, if you would be so kind. There are a couple spell schools that feel really thin, still.
I have but I'm not sure that I can actually say much. At best I could give you my viewpoint but it would be biased by how I see magic in fantasy worlds. Which should be useless to your game world (or the few I know about it reading that thread). And I won't be able to stop mentally comparing to what I do for my mod in which (as much as I hate to mention my mod out of its own thread, so I apologize) some factions use the basic four elements (which "reduces" the spell selection compared to yours, which apparently has 9 open magic schools, but also reduces greatly the overlapping issues) while others stick to only one special type of magic associated in exclusive to their faction. In my case would be Blood for vampires, Attor (short of necromancy) for undead, Faith (I have made the Paladin spellbook so imagine the theme) for a concrete group of humans, and Chi (more like psionics actually) for another group of humans. So now that you know by bias...
I must say that in yours I see lots of magic types. That means great chances of overlapping which by itself may not be always bad (some overlapping is actually good) but that can blur the lines between the different kinds too much (at least until you get the grip of them, as creator of the mod you know best how things work there). Makes me wonder about specialiation and how actually works all the sytem in research (at least Shards are generic).
Intuition: being common grounds, anything goes.
Four Elements: Nothing really special to mention. Air seems to have too much damage and not so much "control". Only Wind Sense for awareness theme. I cannot think of any other neither. But the other elements seem fine and with more clear themes (water still needs some more meat but seems fine too. Maybe some more damage, some more tactical control...).
I read the Light name and I can only think "Aspect of Fire". It may have some deep significance in your mod but reading the spells you have there now, I'd rename it Shadow/Darkness, except for Radiant Visage I suppose. It may be my own bias so as I said previously, just my limited point of view. Focus noticed: Combat. Not convinced.
Ether offers what you mention in the OP: summoning. Other planes must suck though. Demons only?
Summons that are not for combat and/or that go to combat like something more than tanks, could be welcome. The summons can offer great versability to their caster, so depending on the outer planes of your mod, it may be worth considering. Focus noticed: Summons. Seems fine to me.
Spirit is some kind of mix of Mobility and (After)Life. Nightmares reminded me of a spellbook I want to make called Dream (all related to sleep the enemies, have their nightmares kill them and such delightful stuff). Anyway, the moblity part doesn't feel very mystical (Incessant March?) but maybe is because of the names (spirit Walk goes fine). As I mentioned previously, I would go more for some spirit summoning (not Ether related), some movement (but not so much as right now) and buffs. Focus noticed: Mobility apparently? I'd go for spirit buffs and all that shamanic stuff but up to your wishes and lore.
Blood: Dragon Age blood magics aside, I like to think of Maho from Legend of the Five Rings (worthy to check it out for its Elemental spells too) and better of Quietus from Assamite vampires (good old Vampire: The Masquerade). Coating the weapons with poisonous blood, spitting acidic blood, clogging the enemy's bloodstream, blood puppets,... and some more beneficial effects too like purifying any blood related illness. Your spells feel fine altough I myself would focus it more on combat/healing aspects. I don't see so well those about increasing research or production.
But it may be just me. If you consider "blood puppets", I suppose they make sense (not popular spells then). Remember that with the proper sacrifices and high levels of blood knowledge, decimating entire populations (or maybe take total control of enemy champions) is not impossible. Focus noticed: Jack of all trades. The focus on combat/healing would seem to fit better your idea of life/death mentioned in the OP.
If by any chance you found anything useful there... I blame randomness.