I must be missing something, since I have never yet played a race / scenario in which I have ever had, under any circumstances, a financial burden, let alone a horrible one, once the start of the mid-game has been reached -- and it is only then that I can actually start amassing troops.
And I always seem to set my taxes around X% at my homeworld (where X is anything that makes me a ton of cash or a crazy sick overabundance of cash, e.g. anywhere between 25 and 49) and/or any other homeworlds I may have conquered, and set taxes to 0% everywhere else. This is merely habit. I may as well use a RNG to set tax rates on other planets, since setting them to 0% will net me no taxes, but 50% also nets me negligable taxes on anything not a homeworld, and in both cases it doesn't seem to matter since I have too much money anyhow; while 0% will increase growth, but I have never noticed a need for that, it gives me the illusion that by setting taxes to 0%, I am actually making a decision instead of using a RNG. Sadly, however, this is an illusion.