Handlers for checkboxes to select various map features
you only have a difference in two places: query and attribute of dockwidget you are going to check against. so you can pass them as parameters to your score function.

def score(self, query, check_attr):    
    opp_selectedLayerIndex = self.dockwidget.areaOpporunityMap_combo.currentText()
    opp_sel_layer = QgsMapLayerRegistry.instance().mapLayersByName(str(opp_selectedLayerIndex))[0]   
    # Select all features where "Score" = NULL
    expr = QgsExpression(query)
    it = opp_sel_layer.getFeatures(QgsFeatureRequest(expr))
    ids = [i.id() for i in it]

    checkbox = self.dockwidget.getattr(check_attr)

    if checkbox.isChecked():
        opp_sel_layer.select(ids)            
    else:  
        opp_sel_layer.deselect(ids)