Is it worth it to buy a stock after it experiences significant market gains? The answer is, it depends. Some companies don't have much growth fuel left in the tank after a nice run, while others still boast significant upside potential after juicy gains. It's best to stay away from the former, but the investing wisdom according to which we should "buy low" still applies to the latter.Let's consider two companies that have performed exceptionally well recently but still have excellent long-term prospects: Su ...