Really there are only two ways to adjust the height - shimming the existing spring, or finding a new spring. I decided to find a new spring, so off I went to the local hardware store. There I picked up a few different springs that were in roughly the same diameter and stiffness as the springs I have from Zamminc and Hallmark. I picked out one spring in particular that looked promising, but too long. So I took out my handy Dremel, put on the cutting wheel, and started cutting. The key to the process is to cut a bit off the spring, put it on the guitar, and tune it up. If the arm is too high, cut off more. I started with cutting a whole loop, then a half loop, then quarter loops until I got it where I wanted it. As you can see in the pictures below, it doesn't take much difference in spring height to make a big difference in arm height.
Afterwards I wound up repeating the process with a slightly lighter spring that had a more featherweight feel. I'm still deciding which spring I like more, though I'm leaning towards the lighter one.
Two notes - first, wear safety glasses - you're going to break a few cutting wheels and you don't need those in your eyes. Second, expect to break some strings over the course of all the tuning and detuning, so have spares. For good measure I put a fresh set on the guitar once I was done.
