There are building modifiers that can affect galaxy wide build cost. What if all influence modifiers were made percentages? So to subtract 1 influence a month you just reduce influence gain by 33%.
Was intending to look at the viability of using that for empire-wide policies.
The desired inf system is pretty simple, really:
Everything effects rate, no inf stockpile.
All planet hubs beyond the shelter give X inf/level
Every planet edict costs X inf (so each planet can support an extra one edict per level of it's hub)
Every Empire policy active uses Y% of total inf-per-month.
This way, the number of empire-wide policies you can be running at any given time is completely unrelated to empire size - having a dozen planets or one planet, you can still support the same number of them. Meanwhile, per-planet edicts are tied to the size of the bureaucracy, so a highly-developed empire has more flexibility with them that a large but poorly developed one.