As promised, dropped in the new librijndael. Benchmarks say about 3 times faster, but more performance testing will be done.
#!/bin/bash
for f in *.svg; do
echo Converting $f
fname=`echo $f | cut -d '.' -f 1`
rm -f $fname.png
inkscape -z -f $f -w 22 -h 22 -e ./$fname.png
done