Up front, I'll say that I expect this article to generate response from those who don't share my opinion. My reason for exploring this topic is to suggest how important it is for every collector to thoroughly investigate any collecting opportunity before reaching for their wallet or credit card.
To begin, I should offer a definition of what I'm addressing when I use the word variety. Within each denomination of coin we can often find several, if not many distinctly different types. For example, the 1937 Canadian quarter has a design that is entirely different from any previously issued quarters. Collectors would properly refer to this as a new “type” of coin. The 1938 quarter varies from the 1937 only because of the date and is therefore a coin of the same type. Within each type of coin having the same date it may be possible to find variations in the design. These differences can range from obvious to barely detectable. Depending on the significance of the modification, varieties are classified as major or minor. I'm betting few collectors would consider the 1947 quarter with maple leaf after date to be an insignificant variety. The difference between this coin and a “regular” 1947 quarter is quite obvious to anyone who looks at the date and the area around it. In 1951 quarters were struck using dies that produced “ high relief” or “low relief” obverse designs. The lettering in the legend surrounding the portrait is also somewhat different. At a glance, someone who wasn't aware that two varieties of coins were produced in this year might not notice the difference.
Among numismatists, there is often considerable disagreement concerning what makes a minor variety different from a downright insignificant one. The current tendency is to meticulously examine coins in search of the slightest differences. From a purely numismatic perspective it is correct that these minute differences be noted and recorded. That these discoveries result in creating higher monetary values for certain coins is a function of the marketplace and has little to do with numismatic research. My experience has been that those promoting a variety often have some of these coins on hand and wish to sell them for more than the “regular” coin might bring. What the collector must decide is if this variety is indeed worth a premium to own while understanding others may reach the opposite conclusion.
In the early 1960's I was attending a coin show and happened to overhear two collectors discussing the merits of the “one water line” 1957 dollar. As I recall, one of the collectors more or less said that he'd had enough of counting water lines. If the RCM came up with a coin that had the Native American paddling on the right side of the boat then he would pay attention.
If you can add an interesting variety to the collection without paying a premium for it then good for you and nice shopping! Otherwise, before paying a premium price for any variety carefully consider the coin's importance to you. Don't be swayed by talk of rarity or investment potential. My preference has always been to build the basic set first. Once this primary project has been completed, if my interest in the type of coins remains high, then I'll go looking for varieties.
It is also important to remember that as new varieties are discovered and the finds become known the population of coins having this variety tends to grow. In general, it takes time for the market to determine the value of a variety. Collecting varieties is a specialized area of the hobby. Not everyone may be interested in examining water lines or counting beads.
If you are genuinely fascinated by varieties for numismatic reasons then it's possible to have a wonderful time collecting them. If your primary reason for acquiring these coins is to profit from the experience please be warned that the results may be mixed.