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 American Express Company (NYSE:AXP) gained 1.5% this morning after Morgan Stanley upgraded the credit card giant from Neutral to Overweight.

So what: Along with the upgrade, analyst Betsy Graseck raised his price target to $100 (from $90), representing about 15% worth of upside to yesterday's close. While contrarians might be turned off by Amex's solid share-price over the past year, Graseck thinks there's more room to run given the strong tailwinds -- growth potential of OptBlue and the improving economy -- working in its favor.

Now what: According to Morgan, Amex's risk/reward trade-off is pretty attractive at this point. "We believe Amex can win over small merchants with its OptBlue program, boosting US acceptance closer to [Visa (NYSE:V)/MasterCard (NYSE:MA)]," noted Graseck. "Look for 7%/14% rev/EPS CAGR through 2016 as Amex takes share." When you couple that positive outlook with Amex's seemingly reasonable forward P/E of 14, it's tough to disagree with Morgan's upgrade. 

Brian Pacampara has no position in any stocks mentioned. The Motley Fool recommends American Express, MasterCard, and Visa. The Motley Fool owns shares of MasterCard and Visa. 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.