Hi, Jack I fly sailplanes with up to 4m (160", Multiplex Alpina, ASH26) wing span, and never had the need for augmenting roll control with the spoilers.
In this kind of sailplane normally no more than the ailerons is requiered, and if you need some more roll control, you mix some aileron input to the flaps.
However, a friend of mine has a 4.5 m (177") Graupner Discus 2b, and he felt that he needed more roll control, and mixed in some spoiler, like you suggested.
In your case, I would install the spoilers, if you need them for roll control, good, you have them. If you don't need them, use them only as speedbrake.

Michael