Even though the ebuild sets DO_NOT_COMPILE="wifi" if you set USE -wifi, the KDENetwork configure script detects the presence of some wireless tools and decides to compile the KDE wifi stuff any way (on my system this then fails due to a dependency on arts) The only way I could get around it was to alter the configure script and remove the test for the wireless stuff, so I imagine the configure script needs patching.
Created attachment 39985 [details, diff] patch to disable wifi if specified at configure time. I think this patch will help if you make sure to pass --disable-wifi at configure time.
patch works for me. kde-base/kdenetwork-3.3.0 -arts -debug +samba -slp +ssl -wifi -xinerama
This problem no longer exists in 3.4.1.