I cleaned mine every 4rth oil change or about every 12-15k on my old cars. My car just broke the 12k mark and I was running an oiled filter (SPT for 6k) so when I get home Im going to clean mine for sure!
Yes the SPT filter is oiled. Mine had oil in the bag and was so covered in it I had to clean it 2 times before it would stay on the intake!
I bet its nasty.
Ill take pics and such if any one wants.