While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Twitter, Inc. (NYSE:TWTR) surged 3% today after Nomura Securities upgraded the microblogging giant from neutral to buy.

So what: Along with the upgrade, analyst Anthony DiClemente planted a price target of $43 on the stock, representing about 40% worth of upside to yesterday's close. So while momentum traders might be turned off by Twitter's sharp year-to-date pullback, DiClemente's call could reflect a sense on Wall Street that its growth prospects are becoming too cheap to pass up.

Now what: Nomura raised its top-line estimates for Twitter on improved monetization and its adjusted EBITDA view on higher incremental margins. "We believe that the market has now priced in the expectation that Twitter remains a niche social media product," said DiClemente. "We believe risk / reward is much more favorable now, given the possibility that product enhancements rejuvenate user growth; we think ARPU will beat estimates given strength in ad demand, and we believe that incremental margins should be higher than the Street expects." More importantly, with Twitter boasting a rock-solid balance sheet and still-beaten down stock price, the downside seems limited enough to bet on it.

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Brian Pacampara has no position in any stocks mentioned. The Motley Fool recommends Twitter. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.