Personally I would like to make the tree's to be even more focused on certain strategy's then they already are, adding to this the finishers should be stronger imho to encourage finishing a tree rather then just taking all the goodies from every tree and dishing the "junk".
Tradition: tall empire
Tradition opener should unlock terracotta army and rice terraces.
Ceremonial Rites: Monuments should be free, other then that its fine if it doesnt bugg out, for instance as Japan it gives you dojo's and no extra culture.
Monarchy: Perhaps give 1 gold / pop in cap?
Landed elite: Free granary in first 4 city's, +25% food in first 4 city's, +3 food in first 4 city's
Oligarchy: besides the already used bonuses, give a free ranged unit in your 4 oldest city's.
Liberty: wide empire
Opener: unlocks pyramids and hanging gardens.
Finisher: The free GP is great but I would also add -1 unhappiness / city.
Honor: military
Opener: unlocks statue of zeus and temple of artemis.
The culture from defeating barbs is for me the greatest imbalance in this game. Humans are very capable of farming barbs while the AI's dont understand the concept. Every game this policy alone gives me 3-5 free policy's and its always my first pick.
In stead of the culture give 2 free warriors at capital.
Military caste: besides the already used bonuses, give a free ranged unit in your 4 oldest city's.
Gladiators: a free arena in your 3 oldest city's, arena's give +2 culture and +1 happy.
Spoils of war: up the gold bonus to 300% / strenght.
Professional army: -50% upgrade cost, +15% prod for all military units.
Finisher: Can purchase great general from industrial. Unit maintenance is reduced by 30%. Military training buildings give 50% more exp.
Citadels give +3prod, +3science.
Piety: faith + golden ages
Opener: should unlock stonehenge and churches of lalibella.
+3 happy and +1 faith / city.
Unity: all current bonuses, +33% to GA turns.
Charity: temples +25% gold, holy sites provide 5 gold.
Finisher: Choose a pioef belief. Great prophets become 25% cheaper, holy sites provide +5 culture +2 tourism. The religion special buildings get +3 faith.
Patronage: city states and diplomacy
Opener: Unlocks angkor wat and forbidden palace
As others pointed out remove the meeting with all the CS, its not fun.
+1 influence / turn for trade routes to a CS.
Consulates: +20 resting point, +50% influence for performing missions for CS
Finisher: Current effects + Doubles the effect from scholasticism + 2 extra votes in world congres.
Aestics: cultural
I have never even opened this tree, cant judge it atm.
Wealth: gold and trade routes
Opener: unlocks panama canal and taj mahal.
Gives +5 gold in oldest 4 city's, lose the prod bonus.
Protectionism: +20% wealth, +1 gold on trading post and fishing boats.
Caravans: +2 gold / era for every trade route, +1 trade route.
Maritime Infrastructure (rename): -20% purchase costs.
Mercenary Army (rename): had some idea's but I doubt the AI can handle it, better to remove it all together.
I would replace it for: merchants give +4 gold, 1 extra merchant slots in every city.
Finisher: +2 gold and happiness for every luxury resource. Can buy great merchant from industrial. Stock exchange 50% faster to build, +3 culture for every trade route.
Exploration: Expansion, growth and naval
Opener: Unlocks CN Tower and Red ford, keep the current bonuses.
Naval tradition: +1 happy for every lighthouse, harbor or seaport, receive 3 free carracks.
Mercantilism (rename): +2 prod / coastal city, +2 gold for every lighthouse, harbor or seaport, receive 3 free galleass.
Colonization: Newly found city's start with 5 pop, receive 3 free settlers at the capital.
Homestead Act: Get a granary, lighthouse, aquaduct, smith, harbor and monument in newly settled city's.
Pioneer Spirt (rename): Military ships are build 25% faster and all newly build military ships get the promotion naval recon I for free.
Finisher: Can buy great admirals from industrial age, seaports 50% faster to build, get a free hospital in every city, -25% building maintenance.
Knowledge: Science
Openener: fine
Humanism: Up the bonus to 15% science when not at war.
Counterintelligence: +100% spy stealing rate, enemy spies 25% less effective, 1 extra spy.
Securalism: scientist give +3 science, 1 extra scientist slot, great scientists rate +25%.
Scientific Revolution: +100% research agreements awards, research agreements take 25% less turns. defensive pacts give 20 science / turn.
Finisher: can buy great scientist from industrial, research labs 50% faster to build, 1 free technology, +15% science in every city.
Hopefully some of these bring new idea's to improve this already fantastic mod.