I have not yet used Vallejo paint but did purchase some Vallejo weathering system packs at the iHobby show this year.
As the amount of paint in the weathering system packages is so limited, I intend to practice using paint in the larger containers purchased from Hobby Lobby.
That said, I find that Vallejo paint as purchased off the shelf seems to settle just as much or perhaps more than the Testors enamels that I am used to using.
I may very well try out some of the paint mixing ideas posted in the FSM " Inexpensive paint shaker " thread:
http://cs.finescale.com/fsm/tools_techniques_and_reference_materials/f/23/t/162367.aspx