This is an "old" thread by now, but I'm new here, so just seeing it.
I've extensive experience with sourdough. My own culture is at least 10 years old. I've never fed it anything but all purpose flour. I tend to agree with aryaya - just feed it the most affordable, then use your special stuff when making bread! I've made all-white, whole-grain, spelt, etc., etc., but have always fed the started with all-purpose. For my all-white loaf (my favorite), I use a high-protein flour such as King Aurthur bread flour.
That said, I hear a great way to increase sourness in your bread is to feed your starter with rye flour.