James, remember the midvalve is "active" and sees lots of volume, but the base valve sees much greater pressures....that's why it needs to be much heavier.
As Marcus elluded earlier, the amount of change you can make at the BV is rather surprising, at least it was to me. Don't be afraid to go "radical" as you may be surprised with the results. I recently tried a new stack in my Showas...thinking I went WAY over the top and the bike may not even be ridable....well surprise! It was closer to the direction I was looking than anything I have done yet.