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 Morgan Stanley (NYSE:MS) climbed 1.5% on Tuesday after Bank of America upgraded the financial holding giant from neutral to buy.

So what: Along with the upgrade, analyst Michael Carrier reaffirmed his price target of $35, representing about 20% worth of upside to yesterday's close. So while momentum traders might be turned off by Morgan's share-price pullback in recent weeks, Carrier's call could reflect a strengthening sense on Wall Street that the company's prospects are becoming too cheap to pass up.

Now what: According to Bank of America, Morgan Stanley is a particularly attractive short- and long-term opportunity. "We are upgrading Morgan Stanley (MS) to Buy from Neutral, based on a more attractive risk/reward given the recent pullback; earnings upside in wealth management, equities, and investment banking; and longer term upside from increasing efficiencies and capital return," said Carrier. "While there are still clearly headwinds for MS and the industry given the numerous regulatory changes, with the stock trading below year-end TBV and expectations of ROTEs moving to 10/11% in 2015/2016, we view the risk/reward as attractive." With Morgan trading at a clear price-to-book discount to the industry as well, it's tough to disagree with BofA's bullishness.