As teacher that has worked at a private school with uniforms, I have mixed opinions about this.
You have many valid points OP, but what uniform advocates often neglect, is that amount of effort that goes into enforcement of such policies - which is ultimately a waste of time, as that's time and effort (read: money) that goes towards enforcing uniform dress, as opposed to education. Kids try to 'cheat the system' all the time, including cutting or rolling up skirts, wearing ties improperly, wearing incorrect socks/shoes, etc. It's an endless battle, and it's a foolish hill to die on, because it's ultimately irrelevant to the quality of education they receive.
Also, your point about it benefiting poorer students is invalid, because the majority of cases, there is a fee associated with purchasing the uniform; this is a unnecessary cost for clothes that will only be worn for school, when student surely already possesses clothes, and any unnecessary costs are in fact, bad for the poor.
Lastly, a reasonable dress code that allows the students a little bit of freedom, means that you have firmer ground to stand on in strict enforcement;
>strict enforcement = rules being taken seriously
>rules being taken seriously = less infractions
>less infractions = everything runs smoother
To be clear, I don't think uniforms are necessarily bad, but in terms of ways that the school system can be improved, it's literally retarded to focus on student dress, when there are issues are Marxist indoctrination, gang activity, teenage pregnancy, abysmal Math and second language programs, and the general decline in academic performance across every subject.
It's a non-issue OP, and you're literally retarded for thinking otherwise.