One other argument for using clear coats (other than decals) it that some washes flow into panel lines better with the clear coat. I think that depends a great deal on the base coat, Tamiya XF acrylics are terrible for this in my opinion. Tamiya's own product (enamel panel liner) will not flow well at all on top of XF paint.

I have tried using an acrylic wash on top of enamel color, but I did not use any detergent or anything to lower the surface tension, so it had a tendency to "puddle". I think I'll give some of the tips above a try.