Do 衣服 and 衣饰 carry different connotations or are they synonyms? 衣服 and 衣饰 both mean "clothing"; but are they truly synonymous or is the use of each term confined to its own specific context? 

Or is it simply a difference between colloquial and formal speech or between the spoken the written language?
The former refers to clothes in general, while the latter refers to clothing ornaments/decorations (such as embroidery, patterns, etc).