Some simple suggestions regarding the game as is:
I was going to have only two suggestions but went overboard, and I hope you don't mind. The game is great as is, I don't want to seem to imply it isn't.
Inflation:
Having state buyer (in agricultural policy) should have a monthly effect on inflation, particularly when you also control the finance ministry.
If you control the finance ministry should make the Reichsbank help you in the event High Inflation.
Having high inflation should have a passive negative effect, like deflation has.
Values such as nationalism, socialism and pro_republic:
There should be a lowest value for nationalism, as is now it can get ridiculously small.
There should be more ways to promote socialism, I might have missed something in the code but I think only focusing on radio has an effect. If you do end up changing this, there should be a max value of socialism too.
Values such as pro_republic, socialism and nationalism should have a bigger effect when campaigning, maybe as multipliers?
Stahlhelm ans SA:
Having banned SA and Stahlhelm should effect them more so that they gain less during events or when dealing with the reichsbanner.
The strength of SA should be taking more into account during events such as all quiet on the western front, and the threshold for a civil war should be based on the strength of sa + sh, but not take whether they are banned or not into account.