What's the finish of the paint like? If it's not too think I would probably re-prime them to get an even colour and texture all over the models before moving on to other colours.
Do you have any Vallejo acrylic polyurethane primer? It's designed for use with an airbrush so you have a lot more control than using a spray can.
Hm, yea repriming with an airbrush seems like a way to do this for a better consistency. I think if I do a thin enough layer, the details will still show through clean enough.
-With red I'm starting from level zero, and color/technique so I'm happy to dump my old GW colors and invest in some new paint. Those GW pots are awful anyway. Is Vallejo the way to go, and which reds should I get? The gradient of reds on your models is very beautiful!