By their fruits shall ye know them. That's the NT standard.
" Joseph, Esther, Daniel -- none of them would have said "My kingdom is not of this world". "
True, but it does not logically follow that we are now to sit back and allow worldly kingdoms to fall apart -- that's bad stewardship. And no, Elijah isn't supposed to slay the prophets of Baal - the Israelite theocracy has been superceded. But since the NT clearly tells us that goverment officials are "ministers of God" to keep public order, and that we should pray for them in order to live a quiet and peacable life, God clearly still cares about government, even though it's not the theocracy of the Judges.
I'm not sure why we're arguing. If you mean that individual salvation is a much higher priority in God's view, than government (or anything else), then, we already agree. (BTW, that was also true in OT times, not just in this "age").
We can either ignore government altogether, or, we can regard government as a secondary matter with which we must, sometimes, concern ourselves with. Obviously I take the second view. But since you admit that Christians should be good citizens, vote, etc, then how exactly do you differ from me?