Hi Keith! Have you tried shading with the edge of the pencil rather than using the point? Using different weight and even different pencils, you can achieve a whole variety of effects. Also use a Putty Eraser to take some areas away.
taking things a stage further, even try shading with Watercolour Pencils, and coax out some subtle colour with a damp brush.
When I paint, I use the edge of my brush to achieve dry brush effects, and a similar effect can be achieve with the side of the pencil; have a go and lets know how you get on, or if you don't think this helps, then come back to me and we'll try something else.
Good luck and very best wishes,
PA & RSC Wigan / Warrington / St Helens