I'm trying to use a grid mesh with a displace modifier on it to create a terrain. I want to paint in the heights of this hill using the weight paint tool. While this does work, it's hard to control. The blender weight paint tool seems to only add or subtract a value of 1 from a circle around the cursor. This makes it really hard to get an even mid range value. For example, I'd like to create a plateau where all the points have a weight value of .4, but the brush tools make it difficult create anything smooth.
Is there a way to get the weight paint to target a specific value? Alternately, is there a way to get the displace modifier to sample from vertex colors instead of vertex groups?