Silver: Historically, gold to silver ratio had been 1:15. Silver is even more manipulated than gold so current ratio does not reflect the historic norm. And silver has wide industrial uses, some of them can not be recovered.
Gold, Silver, Platinum and Palladium are designated by IMF as monetary metals. They all have prospects to be used as real money or back up paper money as the de facto reserve currency (reserve assets).
GLD: I believe you have not read GLD prospectus in details. It does not nearly equal to the physical gold.
First, it has declining value.
Second, it holds bricks of gold (if you believe they do). How can a samll investor ask for delivery of gold? saw the bricks? (I hope they are not made by Tungstuns)
Third, the prospectus says clearly they hold the rights to delay, cancel the redemption orders. It did not specify how they will liquidate the shares in emergency.
Many, many more.
http://www.spdrgoldshares.com/media/GLD/file/SPDRGoldTrustProspectus.pdf
GLD is a paper game of Wall Street, any one can believe it is real though. :)