The more accurate the data, the more accurate the predictions.
However.
I think a 30 degree change will make a big difference, but only if the wind strength is significant.
Personally I only put the wind in if there is a change of either 10 degrees or 10 kts. This still means that I don't have to put most of the winds in and the forecasts are still very accurate. Also and more importantly I don't have to use my brain that much when I'm in a rush to fill the box up.
FIS.