Primal powers. Not dreams. Dreams are windows, sometimes doors, through which the perceptions of Player Characters may see things they don’t understand. And I’ll let my friend, Jvstin, intrigue you about the magic of Dreams. Check out the power to walk Dreams here.
But the exploration of Primal powers, the clocksprings of the universe before Pattern is an interesting journey for the GM. You can take Corwin’s perspective. Then the Primals might be Vengeance, Rivalry, and Music.
You can take Dworkin’s perspective, and then the Primals might be Art, Blood, Madness, and Devotion. In my campaign, I tried to build Primals that twist through the foundations of the story Zelazny tells in the novels of Amber. Certainly you can tie the Queens that Oberon choose into this entire question. You can twine the spikards, the rivalries between sibling bloodlines, and perhaps more into the question of Primals. The powers of Trump, Pattern, Logrus, and Ghostwheel are all on a more modern and sophisticated level if you plan this way. In fact, what if the Primals themselves are ‘dead gods’ as Merlin describes them? What if they had agendas and aspirations once upon a time? And what if the Amberites are larger-than-life avatars of some of those ‘old battles’ and agendas? Or the building blocks of Shadow might be more wild, more ‘chaotic’ than Chaos itself. Is it worth exploring the parallel between UnderShadow and Underhill, the realm of the Olde Wilde?