Jim: If the roof appears straight and the rafters are all on the same plane, with no undulation or noticeable unevenness, I would make recommendations, rather than calling for repairs. If you do this, IMHO, you will be serving your client well.

2x6 purlins could be installed alongside the 2x4 purlins. Sway braces or struts could be cut under or attached properly to the purlins. Any unnecessary bracing could be removed to remove the clutter from the attic space. It is a somewhat difficult to work in an attic with all the insulation, wiring, ductwork, etc. Sometimes it is also hard to get good lengths of material in to the attic space.

Darrell