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 SunPower Corporation (NASDAQ:SPWR) gained 8% in premarket trading Wednesday after Bank of America upgraded the solar products specialist from underperform to buy.

So what: Along with the two-notch upgrade, analyst Krish Sankar boosted his price target to $37 (from $21), representing about 34% worth of upside to yesterday's close. So while momentum traders might be turned off by SunPower's price weakness in recent months, Sankar's call could reflect a growing sense on Wall Street that its prospects are becoming too cheap to pass up.

Now what: According to B of A, SunPower's risk/reward trade-off is particularly attractive at this point. "The company offers the industry's highest efficiency panel, has exposure to key growth markets globally, and is backed by global energy giant Total," said Sankar. "In addition to utility-scale project opportunities, the company's US-based rooftop leasing business holds long-term value. We see substantial opportunity for the company to leverage high efficiency technology and low-cost Total-backed financing to expand contracted project opportunities around the world." So while SunPower remains just too volatile and speculative for average investors, less risk-averse Fools might want to take a closer look.