A military senate seems overpowered.  It contains extremely effective happiness modifiers as well as tax bonuses.  Wars are expensive and tend to make people unhappy, military policies seem in opposition to this reality.  What I would propose would be to modify colonization penalties (similar in effect, but wouldn't result in all your planets being ecstatic over never-ending war).  And I would remove all the gold bonuses from the militarist branch.  Bonus gold is supposed to be a pacifist benefit, it doesn't make a lot of sense in the military branch.

Positive damage/health/manpower and even science would make more sense.

Also, they seem well short of downsides when compared to, say, the industrialist policies.

Some examples that I think would make more sense/be more balanced: 

Military R&D: -X% science, +X% Weapon damage  Your greatest scientists are co-opted to work on military spacecraft rather than general scientific pursuits.

Pro-war propaganda: -X% gold, -Y% over-colonization penalty.  Nationalist Media is used to rise public opinion of unlimited expansion.

Defense Contracts: -X% gold, +Y% ship building speed.  contracts are offered to civilians.  Increases military production but the budgets tend to be bloated.

I haven't really reviewed all the policies, but from my limited experience the Religion policy that forces everyone to be content is for my money the most powerful policy. I mean, you can just keep yourself happy or content without it, but expanding and growing population are probably the most efficient economic activities and this removes the biggest limiting factors on it.