Came across this today. Wanted to post it here to save others from the frustration.
Contrary to the following technotes:
http://www-01.ibm.com/support/docview.wss?uid=swg21342892
http://publib.boulder.ibm.com/infocenter/cbi/v10r1m0/index.jsp?topic=%2Fcom.ibm.swg.im.cognos.ug_cra.10.1.0.doc%2Fug_cra_id36076ASAdvancedCS.html
The change to either the advanced property(ANS.DefaultVisibileItemCount) or the ansproperties.xml(<property>DefaultVisibleItemCount</property>) file does
NOT apply to items in the Explorer/Data tree. In order to increase the number of items visible there you have to change the package properties.
Solution here:
http://www-01.ibm.com/support/docview.wss?uid=swg21340397
This works for 8.4 and 10.1.x as well.