I am sure that there is a lot more going on in the objective real world than we can monitor with our five senses. I think dreams allow us to engage with the real world and monitor the way it is acting on us.
I like the way dreams present themselves as words and images that are trying to get your attention using your model-making brain's ability to make up stories.
I agree that dreams seem to be involved in laying down memories but I realise that dreaming gives us access to a part of our brain we do not normally have access to.
My interest at the moment is to use my dreaming self (which I also access in shamanic journeying) to engage with the Earth. In my waking rational life I often forget about the Earth, or I get worried or confused by contradictory information. With my dreaming brain I can have access to powerful images of what is going on in the Earth, from day to day.
We forget most of our dreams because we don't have access to those parts of our brain once we are switched to wakefulness. But why we evolved that way is a puzzle to me.
I think that when you go on a shamanic journey, you're allowing yourself to have much more access to your unconscious or your sense of connection within the universe, whatever you want to call that. You've accessed places in your brain that you don't normally. You're still there - it's your brain. But you have access in a way that you normally don't. For me, doing that felt like being in a new environment.