The Porsche 911 Carrera had Cd 0.39-0.32.
All the difference was in refinements to inlets and smoothing the belly.
This is the range of drag reduction you're interested in.So perhaps an optimized,air-tight cooling inlet/grille-block,and belly-panning/diffuser could do it,without really altering the 'look.'
That rear spoiler would be very beneficial.