The biggest change Jim and I made to the BtVS system for Girl Genius involved the drama point economy.
To explain, the heart of the long term BtVS game is how Drama Points are apportioned between the hero PCs (who have high skills and stats and therefore can reliably make heroic rolls in physical/combat actions) and white hat PCs (who have modest skills and stats and therefore have a higher risk of failure and their successes are not as impressive. Both have access to Drama Points, which let the player increase their roll, increase their damage, increase both in righteous fury, or summon a convenient coincidence. White Hats start with twice as many Drama Points as Heroes, can purchase them at half the cost and are more likely to earn them in play.
In short White Hats have a higher variability in their success levels than the Heroes. These Drama Points one of the mechanisms BtVS uses to balance the Heroes to the White Hats. Another is how Heroes (directed by the heroic qualities) are more powerful in combat but not in research, magic or other areas. Heroes are physically superior but mentally equal to and probably slightly less skilled in intellectual pursuits; hence the white hats have non-combat ways to shine. Finally Heroes usually get Drama Points from personal Angst generation (which reduces their abilities when they’re angsty) and White Hats share in that when they help the heroes overcome that angst.
This whole structure is designed for the heroes and white hats to likely balance out in hero points by the end of a 22 session season. This means tracking the drama points session by session.
Not all of this fits for Girl Genius: yes, the Sparks have lots of angst and their allies (our term for white hats) help keep them sane. Yes, the allies have bursts of competency. But the allies are usually reliably heroically competent in one or two areas, and the Sparks are not just physically competent but also brilliant. Finally for what we knew was going to be our player base would not want to track drama points session by session.
Our solution was to remove the long term Drama Point economy and simply state that Heroes start each session with 2 Drama Points and Allies start with 5. They can earn points by heroic sacrifice, angst and angst recovery but those points are ‘use or lose’ before next session. The idea was that this removes some of the ability to store and use points over the season but gained us a lot by way of simplicity and kept the allies as relying way more on Drama Points than the Heroes.
As I’ll get to, we didn’t see all the downstream effects of these changes.