A pre-cured laminate plate for use within a component of a wind turbine rotor blade may generally include a plate body extending in a thickness direction between a first side and a second side and in a widthwise direction between a first end and a second end. The plate body may define a plate thickness between the first and second sides. The pre-cured laminate plate may also include a plurality of channels formed in the plate body between the first and second ends. Each channel may extend in the thickness direction between a top end that is open along the first side of the plate body and a bottom end that terminates at a location between the first and second sides of the plate body such that the plate body defines a reduced thickness between the bottom end of each channel and the second side of the plate body.