Should America withdraw as the world "police / peace keepers"?

In 1945, America came out of the war one of the strongest of all of the major participants.
It began to assume the role of a world police/peace keeper promoting it's ideals and political sentiments in an effort to end future conflicts. Of course, there were other competing forces in the world with differing ideas on the world thus creating new conflicts.
70 years later, America spends amounts on it's military that is more then most countries economies. Money that could probably be better spent.
America has based military units per a number of treaties in countries around the world providing host countries with a sense of security and a lower defense budget.

Is it necessary for America to continue this process?

What would be the effect on current world conflicts if America withdraws it's foreign based forces?

Should America honor it's existing treaties or create new accommodations to meet current world political views?

Would America be or feel more secure if it withdraws?