Production levels of krugerrands have significantly varied since its introduction in 1967
The value of a Krugerrand is based upon its gold content plus a premium. Different sizes of Krugerrand fetch different premiums, and price is also affected by such factors such as condition (uncirculated versus circulated) and special preparation, such as proof coins. From its inception in 1967, the 1 oz gold Krugerrand was intended as a way to invest in gold.
Although slightly heavier than one ounce (due to the copper alloy in the coin), each one contained exactly one ounce of fine gold. Bullion coins, such as the Kruger, allow investors of all budgets to buy gold. When the fractal Krugerrands (1/2 oz, 1/4 oz, 1/10 oz) were introduced in 1980, they continued with marking the weight on the coin rather than the value. So the majority of a Krugerrand's value comes from the gold bullion content. To determine how much that is, you can check the current gold spot price.
All Krugerrands are sold with a premium tacked on, which is for shipping, handling and mintage fees. The premium is higher on the fractal Krugerrands with the 1/10 oz Krugerrand charging the highest premium proportionately. What that means is that you want to buy the largest Kruger you can afford to minimize the portion of your investment spent on items other than the actual gold content. So if you could afford an ounce of gold, you would look to buy a 1 oz Krugerrand as opposed to two half ounce Krugerrands.
Uncirculated or a proof Krugerrand are minted to have an additional numismatic value or a value for collectors on top of the gold value. Both uncirculated and proof Krugers have a limited mintage, or number of coins produced. The proofs also have quite a bit of special handling. The Rand Refinery specially polishes the blanks. Then the press operator at the mint hand loads the blanks, which are then double stamped to produce the highest quality impression on the coin. They also have special features to set them apart for example a frosted finish, as well as more reeds on the edge of the coin.
Proofs sets will also usually come with a numbered certificate of authenticity. All of these factors add up to scarcity, and scarcity leads to a higher price. If you're looking to buy a Kruger for collecting, your best bet is to spend some time with a dealer specializing in Krugers, and understand not only the current value, but how well it has historically held that value, so that you can get your full investment back if you decide to sell. This is less of a concern with a circulated Kruger, since they are a fairly standardized commodity.
Gold Krugerrands do not appreciate every year. However, Krugerrands have appreciated in the long-term. Since the Vietnam War, they rose from $35 to today's values of well over one thousand dollars. Since “Y2k” year 2000, Krugerrands have appreciated about 450%.