It really depends on age, mileage, and type of engine. My small fleet of high-mileage vehicles pre-date synthetic oil, and none have roller-rockers, so conventional is fine, however the reduction in zinc content in the majority of today's oils means I add a bottle of ZDDP at each change. The good news on conventional is that you can often pick up a 5qt jug 'free' after rebate, and filters only run a buck or two.
However, if this car has always had synthetic, or is recommended by the manufacturer, then it's likely a good practice to continue with it.