Is there any way to shrinkwrap half way? As in shinkwrapping but the verts winding up in between the original and the shrinkwrap source. For example, right now I have two bodies. One is very skinny, the other is very muscular. I want the skinny one to be more muscular, but not quite as muscular as the other one, so I want a happy medium. How would I do that?
The modifier accepts a vertex group as a limit, could use a vertex group with 0-100% vertex weights. The modifier can also be applied as a shape key so could do so and then adjust the key.
sort of, you can apply the shrink wrap as a shape key.
if you dont know how this works, there is a button next to Apply on the shirnk wrap modifier that sais “Apply as Shape”, after applying it, go to Object data 
and you will see some options under Shape Key. Select the one called Shrink Wrap, and under there you will find a Slider. play with that.