You certainly want a gloss finish to begin with, to offer the best surface for decal adhesion and to prevent silvering. However once decalled you would apply a varnish coat to whatever degree of light reflectiveness you prefer.
I tend to go for a slightly glossier finish on metal surfaces and on newer aircraft, but a more matt finish on older machines that have suffered the vagaries of sun and weather. (All by adding extra gloss or matt varnish to my standard Winsor and Newton Satin top coat.)
FWIW
Sandy