My current bipolar meds include 600 mg carbamazepine ER (aka Tegretol XR), 100 mg Lamictal, and 600 mg quetiapine ER (aka Seroquel XR).

My Seroquel XR is used as mainly a moodstabilizer. It helps not only with my sleep, but at preventing/curbing mania, depression, mixed states, and even anxiety. One of the better for mixed states! After time, though it still helps with my sleep, the amount doesn't sedate exponentially more than smaller doses. Also nowadays, 50 mg in the morning doesn't make me tired at all. And yet, the addition of 50 or 100 mg more, will help stabilize my mood, if it is rising. Have you ever taken Seroquel at higher doses? Sometimes they even prescribe it specifically for depression, at doses up to 300 mg. For mania, usually doses of 300 mg to 800 mg. The only negatives were waiting to get past the initial sedation and its tendency to increase hunger (at some doses). The latter has caused me some minor health issues, like high cholesterol, though it need not in everyone.

I certainly hope that the Lamictal serves you well. I think it's far more side effect friendly for most, than higher doses of Seroquel. As for my Tegretol XR, I think it's helpful at moodstabilization, but not so much on the depression end.