On Google, it is defined as something "extravagant but superficial display", or "to make something glamorous or showy". That doesn't sound negative to me; however, other sources make it sound as if it's negative by adding the word "ostentatious".
According to dictionary.com, ostentatious is "characterized by or given to pretentious or conspicuous show in an attempt to impress others". Further looking up the definition of pretentious states it is "characterized by assumption of dignity or importance, especially when exaggerated or undeserved".
After reading these definitions, glitz does not sound like a positive connotation to me at all. Is there another way of looking at this particular word that is known to be generally positive?