You might also try alternating you media. For example, if you paint a base coat of acrylic, then destroy some ozone molecules and top coat with a lacquer (which may tend to turn yellow over time) or a suitable enamel. I have also found that GLOSS coats make the best initial base coat. Since the gloss is "slicker" it tends cancel the effects of the wash colors clinging between the "teeth" of the flatter colors. I personally prefer enamel and lacquer basecoats with a similar glossy topcoat, then the decals washes and weathering in an alternate media, then a flat topcoat.
I tend to hate acrylic paint, but I recently discovered that Model Master Acryl (acrylic) flat thinned slightly with flow aid and Acryl thinner, sprayed through a medium duty tip on an Aztek or Model Master Airbrush or sprayed in broad strokes with a Pasche or Badger makes an outstandingly flat topcoat, even over underlying glossy surfaces.
The previous replies are correct. The wash colors tend to tint flat colors, but are more forgiving over gloss. I personally (for what it's worth) don't like to cover the whole model with the wash. I try to use them along edges and seams, around details, etc. This leaves the basecoat basically untouched, but this is not always a workable solution if the washed areas cause an unwanted stain. Trial and error will evolve "your" technique.