A few points from a south-western US perspective:

1) MacCready setting should be close to your achieved average climb. With 'ten-knot" thermals, we often find a climb average of 4 to 6 knots - you have to find them and center them as well as climb!

2) Wind speed and direction often does change with altitude, but this is not a major factor until final glide.

3) The best practice to approach an upwind turnpoint is with the minimum altitude for safety. You don't need to change MacCready setting, but don't carry excess height flying against the wind.

4) If in doubt, I use a MacCready setting of 3 - I have never found zero or 1 to be useful as it has no margin for safety. (I don't think I could live anywhere where a MacCready setting of 1 is the norm!)

Mike