Where I take objection with your assertion though about the world's police force is that, in most situations, there is a tangible benefit to us being involved in these issues. In the case of the issue involving control over the disputed areas in the east china sea, a large portion of our imports must come through that areas on their way to US Ports. If a conflict were to breakout, you could expect prices of all those products we get from china, to skyrocket. This is to say nothing of the fact of what it would do to worldwide markets that would again, affect us.
The world is a more interconnected place today than it ever has been. We rely on free access of goods across the world's oceans. Anything that could threaten that access (pirating in yemen, uprising in Egypt, or even the dispute in the east and south china seas) inevitably can and would have an effect if something should go awry in any of those situations.. And part of the way of exerting influence in these areas, is by use of allies in those areas that are such due to treaties and agreements that have lasted for over half a century. The best example is NATO, which has backed us up on several occasions, and remains an important partner with us in issues in the middle east.
My point being, like it or not, we have to be some level of the world's police force. Does that mean jumping in on every humanitarian crisis? No. But, those treaties that you would rewrite would severely hamper our capabilities in to deal with all these issues that popup.