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 Micron Technology ( MU 0.67% ) rallied 2.5% this morning after Bank of America upgraded the semiconductor company from underperform to buy. So what: Along with the two-notch upgrade, analyst Simon Dong-je Woo boosted his price target to $40 (from $22), representing about 35% worth of upside to yesterday's close. So while contrarian traders might be turned off by Micron's steady price strength over the past year, Dong-je Woo's call could reflect a sense on Wall Street that its growth prospects still aren't fully baked into the valuation. Now what: According to B of A, Micron's risk/reward trade-off is particularly attractive at this point.