I am sure the catch can collects a pretty high %age of contaminants but, obviously not all. After about 30K with my catch can, I have a very slight film of oil on the back side of the throttle body butterfly. It easily wiped off with a lint free cloth. I think it would be a good experiment to see exactly how much the second can would catch although, like suzieque says, more stuff, more poetential problems. If you do it, let us know how it goes.
I believe the only resistance in the system is the PCV Valve. Try blowing through a catch can inlet and see how much comes out the outlet.
06 GCO, Dk Khaki, QDII, Flshing Hi 3rd Bk Lt, MDS "ON" Lt, Airtab Vortex Gens, Debadged, Fumoto Drain Valve, BT Catch Can, Chopped EGR Tube, SRT8 CAI, K&N Filter, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tune App, DS Tuner, Cust tubular hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvr, SRT8 frt/rear bumpers, FRI Sidewinder Cam/6.1 valvetrain, SLP 25% UD Pulley, BBK true 90mm T-Body, SOS Ign Coils w/.060 spark plug gaps, SRT Reps with 265/45&295/40X20's.