I cannot speak for everyone here, but from the previous comments on ET, I have concluded that the common belief is that trading upgrades/downgrades do not produce results of a consistent nature. I did try this early on in my trading, but with only mixed results.
In fact, some have postulated the theory that they believe that some of the analysts upgrades/downgrades are traded contrary by the analyst's firms. IE, they are selling while giving an upgrade.
While this may or may not happen, I personally do not believe trading the news or upgrades/downgrades is consistent in any meaningful way.