I stopped using spray-on varnish because I always got some problem i.e. glossy matt, yellow gloss etc. I now just brush on using Vallejo for gloss or satin and Windsor & Newton for matt. I only do one thin coat, too, because the primer is more important and for that I do use sprays (the most suitable Army Painter colour, but metals get an initial coat of Baufix metal primer from Lidl). Soft plastics get no varnish at all as the acrylics form a protective skin anyway.
More nonsense on my blog: http://battle77.blogspot.com/