Yup. There are times when soul quench is worth casting early to take out chaff or fast cav or something but once in combat and after the end of the chaff wars may be useless. With skink chaff and stuff you usually have two or even three turns to cast out the magic missile and direct damage spells before the TG/slann unit is engaged in combat. Also, often after that the skink priest has burned his dispell scroll or cube and has often died; people seem to pick on him for some reason (they don't like wildform and an eagle or something can charge and take him out) and the stone discipline often ends up putting a wound on him by turn 3 because one often is changing the miscast roll of 7 to 8 or the 10 to 9 to keep the slann's level up and keep the TG from being killed off as fast from miscasts.
My son is preparing for a tournament and looking at matchups for his saurus and Tg units and then considering which common lores to roll into and which high magic spells to give up. He really likes High Magic loremaster giving him 8 spells such that even losing two levels and two spells on a miscast with the slann, he still has six spells and a lvl 2 to cat with. It is all about matchups.
Bascially, what one might do is list out what each signature spell does of the 4 hexes and augments and consider which one, for the casting cost, is most useful in a particular combat. Also, consider just in case which other spells in each lore does one want if rolled for and in what circumstances. Then consider when you might opt for spells in the other 4 lores (like a boosted shem's burning gaze or another lore of light spell to deal with graeter daemons and beasts; fire to deal with regen units, ike trolls; metal to deal with high AS units; death to deal with stuff with maybe lower LD but greater T or resistence to flaming).
Similarly, sit down and consider which of the 8 High Magic spells are worth casting early but less useful later and might be replaced. Soul Quench, fiery convocation, walk between worlds, drain magic and arcane unforging are often the "worthwhille to cast but oftenreplaceable spells ." I list drain magic simply because if one has drain magic and expects to roll for augments or hexes, one might not want to cast it in combat to counter one's own spells unless it is the first spell cast (to stop something put on your unit or their unit.
I don't list tempest simply because I don't see people casting it much, even though it may be under-rated, because in some cases it just doesn't do much and eats up power dice. But sometimes tempest can really be worth casting on units such as high elf archers or dark elf crossbowmen or a slave or clanrat unit that is likely to pitch into combat. Casting it on something like scouting, light flying or skirmishing units with only T3 just to clear it for another spell is sometimes also a consideration. You panic or at least deplete an annoying unit of gutter runners for chameleon skinks or example. The opponent might let it go and the unit hit will be -1 to hit if it shoots or charges something and take some wounds in the process, which is doubly helpful to deal with those shooting skirmish units. That can save a unit of chaff from combat or from being shot up. The thing about tempest is that it is a large template that scatters only D6", so it has a really good chance of hitting the target unit and doing some wounds even if it scatters some. if the units does not have high T or a high AS or ward save.
Another consideration if you roll for beasts and the skink priest has one or two non-signature beasts spells you have the better chance of rolling a spell the priest already has and choosing something really usdeful, or rolling one of the really useful spells you want. This includes an amber spear to deal with something big or pann's pelt for making characters in combat hard to kill or savage beasts for characters to kill stuff.
The miasma and hand of glory combo is huge and underated because of the ability to threaten both spells and get one or the other off, especially with TG against high elves and dark elves where sometimes the boosted versions can flip not just the weapons skill equation, but also the Initiative which can mean striking first against white lions and executioners and avoiding the re-rolls to hit by some units. A Nurgle DP is the best example of where one miasma on hit or one hand of glory on the TG is the difference between hitting on 6's and hitting on 5's., or with an oldblood potentially hitting on 4's if both spells get off. Also, rolling mindrazor might be a game changer against monster and heavy armour save armies.
Of course iceshard is also under-rated in nerfing one enemy unit in hitting yours, but making your unit a bit harder to hit and potentially hitting a lot of stuff on 3's instead of 4's is pretty good.
Earthblood, if they don't have flaming atttacks on the TG is often critical in a battle of attrition, which is often where the TG end up later in the battle and has the lore attribute of restoring a wound on something (maybe that skink priest that took a miscast wound or a scar vet or oldblood in a challenge with something that took a wound). It is often best when boosting T or S doesn't soeem to add as much to a TG unit. The other thing is you can always roll for it and see iff you get flesh to stone which is huge for TG and saurus or, in one case, rolled dwellers in turn one and used it on a white lion horde with the banner of world dragon (BOTWD) to knock out almost one third of the white lions (we play characters get a look out sir).
I love the Wyssan's Wildform, +1S and +1T on TG is almost always helpful in those grinding matches in reducing the rate you take wounds and increase the rate one either wounds something or cut through the AS. 1+ AS and 2+ AS units tand characters hink twice before fighting S6 TG or even S5 saurus, especially if they are only S3 or S4 after the first round of combat and will struggle to wound T5 models or T6 models in the case of the sact vet and oldblood.
