Well, as an economist I have to say that the balance between the single
economic policies is not clear to me.
While I am not sure what exactly is meant by Laissez-faire (this is a term
french rationalists used to describe a theoretical optimum they believed in),
I think it is meant in the way that the state interfere´s in the economy
as less as possible. Yet, historically, that would be interventionism, since no
state ever completely refrained from taking influence. Nevermind.
The serious problem I see is that countries with a more liberal economic
policy did industrialize much faster than others, who tried to influence
the economy more. This was due to the enormous advantage in
information that the private investors (here: "Capitalists") possessed in
relation to the governments. While it is true that railways where heavily
subsidized in most countries, the governments paid the subsidies
because the "Capitalists" told them this would be useful. In the game
however, it is completely the other way around. The player knows of
course which factory will run good, while the "Capitalists" seems to have
no idea what they are doing.
Maybe this is an AI problem and you can make the "Capitalists" smarter.
If not, than I would suggest to alter the effects of the single economic
policies. Every step towards more state influence should have severe
effects on productivity. "Laissez-faire" has 100%, Interventionism 80%,
state capitalism 50% and planned economy 20% (for gameplay reasons,
in reality a planned economy has 1 or 2% in the long run...).
Also a step away from a liberal policy should have an EXTREME effect
on research (maybe not in the cultural field), since most innovations, let
alone inventions, were made by entrepreneurs. So a non liberal policy
should make own research nearly impossible, yet than there should be
a way for the technologies to diffuse from one country to another
(which again would be the historical route).
I had a game where I took a socialist government and yet had the most
modern industry in the world. While this is possible for the time right
after the planned economy was installed, it can not hold true in the long
run, since a planned economy is not good in researching new high tech
industries (yet it is capable of using things which are already there, like
the Nazis in Germany or the USSR).
As a last remark I would like to add that the switch from a even nominal
liberal policy to a planned economy should have severe effect (revolts,
capital problems) on the countries, since there are losers to this. The
same goes the other way around.
My excuses for the long post. Yet, the economist inside is really buged
by things like this...