So, previously I've only run CoC for one shots, and sort of had the attitude that if anyone survives a scenario with their sanity intact that I was doing it wrong.
But now I'm thinking of running one of the classic campaigns with the intention of somewhat more extended play, which means not necessarily picking the most brutal scenarios possible and treating PC's as the victims of one of those slasher/horror films where everyone dies.
One topic that this raises that has never been an issue for me before is PC spellcasting
Hitherto, I've always treated any CoC spell that was potentially useful to the PC's as badly designed, and - with the possible exception of prominent mythos spells like the Elder Sign - something certainly to be kept out of PC hands. Likewise, hitherto, to the extent that I ever thought of PC spellcasting at all, it was to think that in the unlikely event the PC's learned a spell, it would probably be one with face melting consequences and in any event they'd probably never learn more than 1 or 2 of them anyway. All of that is probably still true, even if the investigators do survive a few scenarios.
But in this, am I being 'fair?. Does anyone consider it reasonable and expected for investigators that survive a while to become reasonably competent sorcerers with access to useful magic? It feels like there is enough in the lesser grimoire these days, that you could almost manage to be a D&D style spellcaster if you had the starting POW and SAN to support it and enough time to learn the spells. In particular, I'm concerned with the existence of spells that differ from the typical greater grimoire spells in that:
1) They do something useful.
2) They don't involve sacrificing POW.
3) They don't involve human sacrifice or other SAN destroying prerequisite or consequence (or both).
4) They often involve either minimal loss of SAN or no loss of SAN at all. In particular, there are spells like healing, charm animal, cure blindness, heal, detect enchantment and so forth that are effectively costless and quite useful.
Should I be appalled at that? Should I try to thwart acquisition of any sort of useful spell? Or should I trust that as a practical matter, anyone attracted to that sort of power is eventually going to come to a bad end reading mythos tomes and trying out the contents. In this sense, the 'good' spells might be seen as a sort of bait on the hook. If 'good' spells didn't exist, experienced players or players that have examined the rules would have no reason (at a metagame level or at rational level in character) to pursue spell-casting making the contents of tomes pointless since why would you bother reading one?
And in particular, I'm thinking of preemptively house ruling that casting any spell always costs at least 1 SAN as a means of ensuring that at no point could casting a spell be routine. Does this seem reasonable or am I being paranoid? What are some of your experiences as keepers/players with characters learning more than a single spell or in particular learning spells they were able to use as more than one time panic buttons or plot devices?