Thursday is GURPS day! When I remember.
I've been thinking about College Ritual Book Magic recently. We're using it in my online group's Chaos Scar game, so it's getting playtested a bit.
One possible issue that has come up is that there's no value to getting a grimoire of a spell with a positive value more than its prerequisite count. I wrote it that way to discourage people from putting 1 CP in a bunch of difference colleges and then cherry-picking the best spells with expensive grimoires. Which is a good goal, but it also means that there's no value in finding the Archmage's grimoire of Fireball +6.
I'm throwing this out as a possible fix:
A CRB spellcaster can use a grimoire to give a bonus on casting a spell in a College that she has at least 1 CP in. If the sum of grimoire bonus and spell prerequisite penalty is more than 0, then casting that spell is somewhat difficult, and the spell costs additional energy equal to the net bonus.
If a CRB spellcaster uses a grimoire to provide an effective skill on a spell greater than her Thaumatology skill, then she doesn't fully understand the process involved. She can still cast the spell at higher skill, but any failure to cast the spell causes an immediate roll on the Catastrophe table at her current tally.
These two effects combine if the CRB spellcaster is subject to both of them.
I think these two rules get the feeling I want. It's possible to use high value grimoires to cast spells at high skill level, but it's energy intensive and possibly dangerous. On the other hand, a focused spellcaster with very high skill in a single college can cast some basic spells without a problem, even if they don't understand the underlying magical theory. Anyone who wants to cast spells with huge prerequisite counts needs both a powerful grimoire and a lot of skill in Thaumatology if they want to be safe and successful.
What I need to next is rationalize prerequisite counts, but that's a rant for another day.