This does not answer your question as such, but from what I have found the user-defind counters are not that well supported at the moment.
I, too, have used them to monitor a number of different parts of my policy. The only way I have found to graph them so far is a bit of a hack job. What I have done is make a block page that has the various counters I want to monitor. this is then triggered by a specific rule for my monitoring server's IP. I then have a shell script that goes to my blocked page, and pulls that data out and puts in to RRD, and I then graph that data from there. I can share the scripts if you are interested in how I've done this?
Example of what the graphs look like, the solid blue is our whitelist against the left axis, the light blue line is our black lists against our right axis and the red line is the 95th percentile.