Gold Banknotes

[proof27]

Can any one explain what's with these gold banknotes? Is it a gimmick thing or do people seriously collect these? Do they go up in value? I've seen heaps on sale , just never understood the concept.
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[Mister T]

They seem like a gimmick to me - I don't think I've ever seen a coin dealer selling one.

[Australian coin]

they are in the wedding gift section of the Perth mint site http://www.perthmint.com.au/catalogue/wedding-gifts.aspx
I am not interested in that stuff

[ginkaku]

Given as lucky money.