At The Motley Fool, we poke plenty of fun at Wall Street analysts and their endless cycle of upgrades, downgrades, and "initiating coverage at neutral." While the pinstripe-and-wingtip crowd is entitled to its opinions, we've got some pretty sharp stock pickers down here on Main Street, too. (And we're not always impressed with how Wall Street does its job.)

Given that, perhaps we shouldn't be giving virtual ink to "news" of analyst upgrades and downgrades. And we wouldn't -- if that were all we were doing. Fortunately, in "This Just In," we don't simply tell you what the analysts said. We also show you whether they know what they're talking about. To help, we've enlisted Motley Fool CAPS, our tool for rating stocks and analysts alike. With CAPS, we track the long-term performance of Wall Street's best and brightest -- and its worst and sorriest, too.

Great minds (don't always) think alike
The economic recovery is in jeopardy. High gas prices have sent consumers reeling. So clearly, now is a good time to invest in … credit card companies? It sounds crazy, but that's just what two of the biggest names in investing are doing this week. On Tuesday, I told you about how Warren Buffett's Berkshire Hathaway (NYSE: BRK-B) has been snapping up shares of MasterCard (NYSE: MA). This morning, we learned that another big investing name -- Goldman Sachs -- has taken a liking to American Express (NYSE: AXP).

After taking a look at the big names in the field -- Visa (NYSE: V), which it already recommends, and Capital One (NYSE: COF) and Discover (NYSE: DFS), which it still refuses to recommend -- Goldman came away with just one idea that appeals to it: AmEx. As reports this morning, Goldman says that "given its spend-centric business mix, [Goldman] expects continued top-line growth to be aided by further spending by high-end consumers and growth in its international franchise." In other words, if the echoes of the Great Recession are still ringing in the ears of average Americans, "the rich" are still spending, and their currency of choice is the AmEx card.

But is Goldman right?

Let's go to the tape
We've been tracking Goldman's performance on CAPS for close to 18 months now. So far, the banker's stayed away from most credit card networks, but its only actual "buy" rating -- Visa -- is outperforming the market. So score one point in Goldman's (and AmEx's) favor. That said, I cannot get behind Goldman's "buy" rec this morning, and I'll tell you why.

The first reason is Goldman's record: How do I put this gently? While ranking (barely) within the top 20% of investors we track, Goldman really isn't that great an analyst. Visa may be producing profits for this banker, but overall, fewer than 50% of the recommendations Goldman has put out over the last 18 months have actually outperformed the market.

AmEx -- go ahead. Leave home without it.
The second reason has more to do with AmEx itself than with Goldman. You see, I actually agree with much of what Goldman is saying about the credit card companies today. I agree that Capital One isn't growing as fast as investors might like. I agree that Discover isn't any better -- that it was a pretty pathetic credit card company when Sears (Nasdaq: SHLD) introduced it 26 years ago, and that with long-term growth prospects of 6%, it isn't much better today. I disagree that AmEx is a buy, however.

As I mentioned earlier this week, I see two reasons why Buffett declined to double down on AmEx last quarter when he was shopping for credit card investments, choosing MasterCard instead. For one thing, Buffett already owns enough AmEx shares to choke a horse. For another -- the valuation on AmEx shares just doesn't look attractive.

Sure, Goldman-buy-rated AmEx is growing faster than now-neutral-rated Cap1 and Discover. But it's not growing all that fast. Whether you value AmEx on price-to-earnings or enterprise value-to-free cash flow, either way, the stock's 14-ish multiple to profits seems expensive relative to AmEx's 10% long-term growth rate. Finally, the stock's 1.4% dividend yield may be better than the payouts at Cap1 and Discover, but it's still too small to make up the difference and make AmEx a buy.

In short, in order for AmEx to deserve a place in investors' wallets, it will need to either grow a lot faster than most people think it can, or decline significantly in stock price. Shareholders would be thrilled to see the former happen, but personally, I think the latter is more likely.