With any envelope (velocity, volume, opacity, pan etc.) if you Click and Hold the left mouse button on a point you can use 2,8,4,6 on the numeric pad to move the point vertically or horizontally. The precision depends on the size of the track (ie the bigger the height of the track the smaller the increments from using the numeric pad). If you click+hold in between two points you can adjust both the points at the same time. If you select multiple points you can use move all the points at the same time.

With audio tracks once they are at a certain vertical magnification you get .1dB precision.

This technique is great for me because it means I can ajust a point vertically without changing it's place in time.