Glenn, as I think you already know, generally when people paint with Vallejo and similar paints they apply them in sequential layers with the paint diluted (sometimes
a lot). But in case you haven't read anything that made this clear while the paint can be heavily thinned - just like in a wash - you don't apply it that way, instead you only load the brush lightly (damp brush, not wet) and carefully paint the thin, transparent colour exactly where you want it to go.
The beginners' guide to using Model Colour in this way was written by Mario Fuentes a few years ago which used to be available as a download on the Vallejo website as a PDF but doesn't appear to be there any longer. It's the basis of the multi-lingual section in the Vallejo colour chart and while the text isn't in English the illustrations showing highlighting and shading in diagram form make the gist of it clear. They're easier to read in the PDF version of the leaflet which you can find
here.
Most of the text is now on
this page on their site (under
Painting figures with Model Color) along with some other guides that are worth reading too.
Another good ground-up guide to using this sort of paint is on the Andrea site,
here.
You
can do true blending in acrylics - wet blending - but generally only on small areas. If you want to play with doing this over larger distances it's probably best to buy a blending medium or retarder to help slow down the drying time and improve brushability. These products can tend to increase gloss a little so you may end up needing to rely on a matt overcoat of some kind if you use one much.
In addition to problems of application it looks like there may be issues with the colour mixtures/choices but with smoother transitions these should look better anyway so probably best to work on the technique first, then think about colour if necessary.
Einion