Got a pure Dreamer in lvl 44..
Made the Char melee, but I'm sure it's good for range/magic. Use Sands of Sleep if you wanna make a magic or range.
Distortion Wave, and Distort Reality. Those are really life-savers if you're in trouble. Distortion Wave slows, and Distort Reality petrifies for some time. Really worth using. The Phantom Strike is also really great.
The Nightmare is OK, but you gotta be pretty high lvl, before it's really worth something, and thats really a shame. In act 1 and 2 it was really a great help, it gets the hypno skill, which is really awsome when there's more than one enemy.
The Trances can also become real kickass, but thats gotta take a lot of points, so i chose just to focus on DWave, DReality, and the Nightmare, and that's working really good for me.
Hope you can use anything i just wrote, and good luck with the Dreamer.
*EDIT*
Oh, and equipment. The spells costs pretty much mana, so either use robes if you are range/Magic, or find some armor that boosts your mana greatly.