Is there a conventional metaphor or phrase that just hits this meaning:good-looking yet useless?
Of a person
Webster's: "an attractive but stupid woman"
To my knowledge this is a reference to The Great Gatsby meaning a woman who is pretty yet blissfully ignorant. Perhaps it predates that?
Webster's: "not real or sincere" [i.e., superficial, malleable]
Webster's: "a young attractive person who accompanies a usually older person at social events"
Slang: a spouse who is valued for superficial reasons.
Of an object
Webster's: "something of trifling appeal" [lacking in significance or solid worth, frivolous]
Webster's: "a piece of jewelry or an ornament that has little value" [therefore shiny, aesthetically pleasing... not useful]
Webster's: "something that lends grace or beauty" [Webster's example sentence reads: "The columns are there purely as ornament—they have no structural function."]
Dictionary.com: Syn for Oranment, Trinket
Clearly these aren't all perfect fits as they stand by themselves, but given the proper context they could all be used to convey a sense of useless splendor.
Edit: I removed a couple that would have required more finesse to work into the context.
In vernacular English, "dust collector". Something which just sits there, does nothing, and has to be cleaned semi-regularly to remove the dust which settles upon it. Also implies something of low value:
- When commenting about Aunt Amelia's extensive collection of floppy-eared rabbit
dust collectorsUncle Wilmer often said philosophically, "Well, they keep her happy - and the durn things didn't cost much...".
Share and enjoy.
Gold plated turd - something that is essentially useless but has a layer of gloss to make up for it.
I offer gimcrack. As defined by Meriam-Webster [http://www.merriam-webster.com/dictionary/gimcrack]: a showy object of little use or value.
Also gewgaw at the same reference.