We should, can and most of the time do communicate with God...

We should, can and most of the time do communicate with God directly. To my knowledge, angels are not necessary for anything. But God's creation is abundant, and asking "Why angels?" would be like asking why there are thousands of varieties of trees or stars, when we could get along with so much less. God Himself told us many times that He was sending angels to love and care for us, so He is the one who brought them into our lives. Therefore, even if we don't understand their entire purpose, I vote that we pay attention to them.