Maybe this is obvious, but nobody has mentioned it. When you roll a ceiling, do you do stripes or sections?
When I'm concerned about roller marks, I'm putting on 18 inch wide stripes all the way across. When I run out of paint, I reload it and continue the same stripe. When I reach the far wall, I walk back and start a new stripe. That's the surest way I know to keep a really wet edge.
Preferable to go short way across room. Preferable to go perpendicular to light source. Preferable to go perpendicular to room entrance.
Paint does make a difference too. You'd think special ceiling paints would work better, but no. In my experience, they are just more expensive. Stick with the cheap flat stuff.
As for the sprayer, I don't use it on ceilings, but just get one anyway. I have this one:
http://www.lowes.com/pd_295429-48690-LTS+15_0__?productId=4745129
It won't last as long as the Titan. The Titan is made to be rebuildable, so you can kill it over and over again and it just won't die. But if you just want to put your toe in the water, you can definitely make some money on a $300 investment. It'll pay for itself in one job!