"in theory taxes should go down"
"the overhead costs of running fire, police, etc. remain about the same, so it should become cheaper per person."
Should?? You seem to have a lot of faith in the benevolence and efficiency of government.
Not really. If the government is going to raise taxes to pay for more crap they shouldn’t be doing, they’re going to do it anyway. More people in the city should actually slow the bleeding, because they’ll have more revenue. Also, if more conservative-minded people move in, we could replace some of the bums that are in city government.