NAPERVILLE — The four Republicans running for Illinois governor agreed today that the state needs to cut spending and change its tax structure, but they differed on how best to do so. Sens. Bill Brady and Kirk W. Dillard, businessman Bruce Rauner and Treasurer Dan Rutherford faced off in a debate that focused heavily on Illinois’ struggling economy and how to improve its business climate. All four candidates said they support allowing a temporary income tax increase approved in 2011 to roll back as …