A few days ago I posted a topic on magic in AH, and I decided (perhaps wrongly) that is would be more appropriate to start a new one that bump the old on account of what I came up with. I've thought a lot about it and I think I've found the best way (for me) to handle spells. I'd like to get some input from other folks on things I might not have thought of, etc.
The primary issue with spells is how combat spells are made almost entirely obsolete by magical weapons that are superior and are obtained from a more beneficial deck to shop through. Non-combat spells, in general, offer nice utilities that are sufficiently unique and helpful to justify the costs of casting them. Therefore, this rule only applies to combat spells (in fact, it can only apply to combat spells).
When you prepare to cast a combat spell, instead of rolling the lore check to see if you succeed, then adding the modifier to your fight check, you simply replace the fight check with your lore check and add the number of dice automatically. So, when casting whither, you would pay 1 sanity, then roll the lore check, adding +6 to make up your combat check (ignore the casting modifier). IMO, this approach is thematically appropriate and mechanically superior - most of the spells don't represent things that you manifesting to fight with, they represent a one time casting of a spell that has an immediate effect, so logically lore would apply more than fight would. Additionally, the "spell fails" is still thematically covered by the possibility of rolling no successes on your combat check, this just removes the need to make two different checks when you cast a combat spell. Mechanically speaking, high lore investigators (i.e. spellcasters) would receive an average of 2 or 3 additional dice to use for their combat check, depending upon the specific circumstances. This also enables them to safely keep their Wills high over their Fight stat, reducing their susceptibility to sanity losses while maintaining high burst potential. IMO, the lack of casting checks and the higher number of dice is very well balanced by sanity cost and the "this combat" restriction.
Now, this is extremely simple and works well for when an investigator is attacking only with spells, but what about using a weapon and a spell at the same time? There are a few ways to go about this, but it requires more extensive play-testing. This is the main thing I'd like input on. In any case, this is when the casting modifier comes into play - because attempting to do both in a single round of combat taxes your focus.
Option 1: You use only your Lore, adding the combat bonus from both the spell and the weapon, but it is then modified by the casting modifier of the spell being used.
Option 2 : As above, but use only your Fight instead of only your Lore.
Option 3: You use 1/2 your fight and 1/2 your lore, rounded up, then modified by the casting modifier of the spell.
Now, my only balance concerns for this houserule are in relation to Daisy, as well as Dexter's and Harvey's PS successes. The sanity reduction is really too beneficial, it allows those three the potential to have extremely broken spell combos and whatnot... And the above rule even blows them further through the roof. So I propose this simple houserule to bring them (particularly Daisy) more in line with others:
Instead of always reducing sanity to cost to cast spells by 1, they instead can reduce sanity cost of casting a spell by 1 once per turn (just like Harvey's and Micheal's abilities). This is still quite beneficial, but not nearly as broken. It helps bring Daisy down to the power ceiling of the other investigators, although she is still extremely good.