"A new life awaits you in the Off-World colonies. The chance to begin again in a golden land of opportunity and adventure: New climate, recreational facilities - absolutely free." (Blimp ad from street scene in Blade Runner.)

Firstly, my apologies if this has been brought up elsewhere - I'm new to this forum and I know there are whole categories I haven't been able to find yet.

Allow me to briefly explain why I feel that players should have the option to set individual colonies' tax rates and how this could actually reduce micromanagement.

Every world in the game has its own strengths and weaknesses. I like the idea of the global tax rate and don't think it should be discarded. However, I do not like having to adjust my global tax rate every time I establish a new colony (and then re-adjusting and checking all of my morale levels once its entertainment net is built) or when one planet starts to get into morale trouble. It also seems just plain more realistic to allow different planets to be taxed at different levels; would you move your family to Mars without some kind of serious financial incentive?

A set of three options on the planet details screen would solve these problems, make it possible to get the most out of each colony, and actually reduce the amount of time you spend adjusting your global tax levels:
a) Set planetary tax to global level (default)
Adjust tax rate manually (displays a slider like the global one)
c) Auto adjust tax rate each turn to keep morale level at or above [input box]%

I would probably use c) exclusively. Knowing that I could count on at least a minimum morale level, that's one less thing I have to keep careful track of. Or, switching to option , I could tax one colony to the max while defending it against attack, then reset to peacetime levels when the threat is gone, without disrupting every single planet in the empire and a tedious readjustment afterwards.

This sort of auto-adjuster option would be good for the global levels, too.
Taxes: "Auto adjust tax rate to keep the lowest planetary morale level in the empire at or above [input box]%"
Spending: "Auto adjust spending rate to keep the empire's income at or above [input box] bc"

Knowing that I could set spending to keep me out of deficit, or so that I would always have at least enough credits on hand to quickbuild a given ship type, would mean a lot fewer trips to the policy screen for me. I probably spend more time worrying about these things than most players, but with the defaults set to use the global levels, players who don't want to use it wouldn't have to.

One more point in favor of individual tax rates is that if you do micromanage your taxes in the early game, when every single bc counts and you only have a few planets to keep track of, you'll end up with a few more bc to spend when you need them most. Of course, so would all of the AI factions...