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

What: Shares of Alliance Data Systems (NYSE:ADS) gained 2% today after Nomura Securities upgraded the marketing company from neutral to buy.

So what: Along with the upgrade, analyst Tulu Yunus planted a price target of $300 on the stock, representing about 17% worth of upside to Friday's close. So while momentum traders might be turned off by Alliance's price weakness in recent months, Yunus' call could reflect a sense on Wall Street that the company's growth prospects are becoming too cheap to pass up.

Now what: Nomura raised its 2014 earnings-per-share view for Alliance from $12.32 to $12.63 and its 2015 outlook from $14.24 to $14.78. "It's certainly not new news that ADS's PL portfolio continues to grow at a rapid pace," said Yunus. "That said, our analysis of the pipeline suggests that the file's growth will reaccelerate and reach new highs in the 30%+ range later this year. We expect shares to rival their 52-wk high as estimates ratchet higher yet again." Given Alliance's still-hefty debt load and 30-plus P/E, however, I'd hold out for a wider margin of safety before betting on it.