I've never been huge on mixing lipsticks. It's for a kind of silly reason, actually: when you apply the second lipstick over the first, the colors mix on the end of your lipstick tube. It's only in the past few months that I've admitted that you can just wipe the lipstick off on the back of your hand, and the small amount you waste in the process is Not the End of the World.
How did I reach this conclusion? I found a great combination: MAC Party Parrot lipstick with Viva Glam Nicki on top, concentrated primarily in the center of my lips.
Party Parrot, Viva Glam Nicki, Party Parrot + VG Nicki
The colors combine to create a beautiful pink coral, very similar to MAC Impassioned. And actually, VG Nicki is a great layering lipstick in general; it looks amazing on top of dark fuchsia lipliners and under soft pink glosses.
Admittedly, I look a little zonked in the header image. (I throw my makeup on at 6am several times a week, and it shows.) But I think you can see how much dimension and pop this combination has!