In your opinion when it works its legitimate and when it fails its bad and you want to filter out those wrong signals. This understanding is wrong.
There are different indicators. You are using MACD. I use RSI.
A divergence in MACD may not be a divergence in RSI.
Price movement is the same in both cases. But why is one indicator showing a divergence where as the other is not. Now can u say that One indicator is legitimate and the other is not ?
And how do you know that price and indicator will diverge only when momentum is shifting ? And basically what is momentum shifting ?
Divergences occur depending on formulae used in the indicator in regards to price movement ( OHLC positions in the data point ).
During a consolidation phase, when price is moving sideways , indicator may move down. This does not mean that momentum is shifting. Or even in a Uptrend if the price is closing near the low of the data points, you may see a divergence in the indicator ( this happens when the indicator is calculated using OHLC values ) , whereas another indicator which is calculated only using the closing values of the data point may not show the divergence.
Just like above there are different reasons why divergences occur in different indicators. Divergences need not mean shift in momentum of price.