....have become, roughly, "Different systems at different times for different people with different cultures pursuing different goals."
I believe in being principles-driven on a personal level, but on a large-group level it needs to be recognized that every generation faces different challenges.
I suppose if you paint with broad strokes you could say a few policies are almost always good, but even then that disintegrates if you try to nail down the particulars.
Let's say you're building a parliament from scratch in a new nation. How easy should it be for the members to deadlock?
This is not at all an easy or trivial question, and it has huge implications. Nations have at times lost everything by having a deadlocked government in time of crisis. The flipside is that unchecked authority in the hands of the current ruling party can quickly lead to either partisan strife where the two dominant parties keep reversing each other's policies as fast as they can get implemented, or despotism if rule is consolidated consistently in one side's hands.
So, how deadlockable should your parliament be?
It's hard to say.
Not to mention that you don't have full and complete control of your own policy... oftentimes it's dictated by circumstance. It's basically inconceivable that no first-world government on earth would like to run higher interest rates through their central bank if they were in a vacuum, but there would be a massive influx of carry trades if you were running a stable government with high interest rates and no currency controls. Thus, you'd instantly have a lot of speculative money -- probably more than you knew what to do with -- and you'd have significant debt payments to service. Your currency would grow stronger in international trade markets, which would make your citizens import more and export less.
...so everyone's got these really low interest rates. For most nations, it has less to do with independently coming up with financial policy, and far more to do with the decisions made in D.C., London, and Brussels.
At one point, I thought there were right answers in politics. There still might be a few. But I think you've got to at a people's current state, culture, and what their goals are (or could be) -- and build around that.