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 First Majestic Silver (AG -0.29%) slipped about 0.5% in pre-market trading Thursday after TD Securities downgraded the silver explorer from buy to hold.

So what: Along with the downgrade, analyst Daniel Earle reiterated his price target of C$15.50, representing about 24% worth of upside to yesterday's close. While contrarians might be attracted to yesterday's earnings-related pullback, Earle thinks First Majestic's forward valuation is no longer all that attractive relative to other silver miners.

Now what: According to TD, First Majestic's risk/reward trade-off is pretty balanced at this point. "Q4/13 cash costs were slightly higher than we had anticipated, while capital expenditures were in line," noted Earle. "With the company expected to generate negative free cash flow in 2014 and as it is now trading in line with its peers on our estimates, we are downgrading our recommendation to HOLD (from Buy)." Of course, with First Majestic still off about 30% from its 52-week high, that bearishness might provide resource-savvy Fools with a shiny long-term opportunity.