Not all coins appreciate in value more than the metal they contain & many even fall in value due to the large premium paid initially. For example if you pay $100 for a 1 ounce Silver coin and the value of the underlying metal is only $22, there is a long way for the price of the coin to fall if secondary market demand isn't strong for that particular design.
The Olympic coins are a good example of those which have not performed well due to low demand. I've bought multiple Gold coins in the series for spot price (basically no premium paid for the coin over metal content).
The kilo silver coin sold in the year 2000 for $860:
http://shop.auspost.com.au/INTERSHO.../en_AU/assets/document/1239072250-bull256.pdf
Silver spot price was around A$8 an ounce, so the value of the metal in the coin was around $255.
I recently sold one of these same coins for $950. Only $100 more than the 2000 price, but Silver is now A$22 an ounce. So the coin has appreciated by around 10% and Silver by around 175%. You can see in this example you would have been much better off buying low premium silver bars instead of the coin.
Of course it doesn't always work like that. Some premium coins I bought in 2011 held their value despite a large drop in the spot price of Silver.
My recommendation for the casual silver/coin buyer would be to buy mostly 1oz mintage limited BULLION Perth Mint coins (at or near issue price, usually $5-10 premium over spot for a 1 ounce silver coin), those such as the Kookaburra & Lunar series coins are a good place to start. The premiums on these tend to appreciate over time. If buying Gold then just stick to low premium, well recognised bars of the stuff and avoid any high premium coins.
For those a little more adventurous there is an auction in Melbourne this week that is worth a look (I would be there and bidding on some items if could do so easily in person):
Catalogue:
http://downies.com/aca/PDFs/319A/Auction_319_RAM_LR.pdf
Story:
http://www.smh.com.au/money/investing/master-coin-sale-worth-cashing-in-on-20150519-gh1fgx