The best reason to eat well in Preston is the South Asian dining scene, which is genuine rather than tourist-facing. The streets around Deepdale have a concentration of good Pakistani and Bangladeshi restaurants where the cooking is the real thing — seek them out rather than the city centre equivalents.
For Italian, Bello on Friargate has been feeding locals for over 30 years, using simple seasonal ingredients with solid vegetarian options. For something with more occasion, Farington Lodge, a Grade II listed hotel just south of the centre, has a garden restaurant serving contemporary British food.
The rest of the centre has the usual mix of pubs, fish and chip shops, and international restaurants. Nothing to travel for specifically, but you won't go hungry.