not simply opinion. i believe there is literature on the subject somewhere - roaches simply have a more suitable nutrient ratio. im sure crickets work fine though if youre going for simplicity
and varying the diet cant hurt
plus it'll give you an excuse to go outside and catch some bugs!
try putting in sticks of varying diameter and (this worked when i had an eggbound female once) get some textured bark and try cutting it into strips about 1 or 2 cm wide. the texture of the surface may contribute to her laying. oh and try making it so that the bark surface faces northish and gets a lot of light during the day. shes looking for a place that will incubate her young well. that means warmth.
how often do you spray?