Using Canned San Marzano Tomatoes Vs. Regular Canned Tomatoes I have never used San Marzano tomatoes yet. I recently bought a cookbook and most of the recipes call for San Marzano Tomatoes. They are more expensive. Is it really worth paying the extra money for them? 

USA Prices

$3.82 28 oz. can Centos brand D.O.P. Certified San Marzano tomatoes From my local market. D.O.P. Certified is guaranteed they are grown in the Mount Vesuvius Volcanic soil. 

$1.44 28 oz. can Contadina brand tomatoes from local market.

What is so special about these? I get mixed reviews on the net. One person says it is a bunch of high brow people showing off and others say you can take a can of these and grind them in a food processor and drink it like tomato juice.

I would like a concrete answer from somebody that has used San Marzano tomatoes enough times to say definitely worth it or not. I will be making Pizza Sauce and Spaghetti Sauces.
San Marzano tomatoes are generally preferred for Italian tomato sauces because they are denser, fruitier, have a slightly lower acidity, and break down well when cooked.  I've made both fresh and fresh-cooked tomato sauces from the San Marzanos my mother-in-law grows, and would prefer these over just about any other tomato variety for sauce-making (dry-farmed Early Girls are also pretty good).

However, in my personal experience trying several of the canned and boxed varieties of San Marzanos available to me, they're not worth paying more than double what more common varieties of tomatoes cost.  For example, last week I made my standard "quick tomato pasta sauce" using boxed San Marzanos, and did not find it notably better than other high-quality boxed tomatoes (such as ones from Pomi) which cost $2 less. My judgement is that many of the qualities which make them a superior tomato when cooked fresh are destroyed in the canning process.

On the other hand, you're comparing them to Contadina, a rather low-quality brand.  Given that specific comparison, I would expect the San Marzanos, even the mass-market Italian brands, to be notably superior in quality.  So if that's your actual comparison, I would say go for the San Marzanos.

According to an article in Cook's Illustrated from several years ago (CI archives are behind a paywall, so no link), this is partly because San Marzanos, like other imported tomatoes, need to be canned at higher temperatures in tomato puree instead of at lower temperatures in tomato juice due to obscure US produce import restrictions.  So it's also possible that canned San Marzanos can, in fact, be excellent, just not the ones commonly available in the USA.