That port on the PS valve cover should be sucking IN, not blowing out, so the oily air inside of it should not be able to flow out and into the intake duct. It's supposed to let the crankcase pull in filtered air from the intake duct. I'd imagine this to only really work at idle/closed throttle when vacuum is at a minimum. I've never investigated, but maybe there's a check valve in it (I don't see how it'd work without a check valve) and it's stuck open, letting intake vacuum suck oily air out of it and into your clean air intake tract?
This wouldn't work. Well, it'd kinda work, but only cuz the PCV outlet (the port on the DS valve cover) and the vacuum in the intake tube would overpower the PS trying to draw air in. If anything, you should route it to the port on the manifold so it'd be behind the TB. If you route it going into the intake tube, ahead of the TB, that oily air would eventually gunk up the TB.
I've never polled the masses, but I'd have to guess that if most people do this, it's because most don't know how the system is supposed to work. It'll still mostly work, but not as efficient as it could, as it was designed. The factory design works very well at evacuating the crankcase and reprocessing the gases without venting to atmosphere so you have to smell the oil- why screw with it? The problem is that the LS moves excess oil through the PCV system. You just need to filter this oil from the air as it flows in it's originally designed form, not try to completely change the flow characteristics.
Sounds like the same as outlined above- lesser efficient due to the PCV overpowering the fresh air inlet. With boost, all bets are off and everything changes. So, the "lesser efficient" tied-together valve covers only comes into play when not in boost.
This is how it is from the factory. So, the PO didn't change anything here or take any shortcuts.
IMO, I'd stick to the factory design and just filter that one circuit- the dirty side that SHOULD have oil in it (although it's a lot/too much). If the other side is blowing oil into the intake, then I'm inclined to think there's a problem over there, like the stuck check valve theory previously mentioned. My system is stock but with a catch can on the dirty side. I run mine hard, so lots of engine load with WOT and high RPM. My intake tube is clean and dry and I consistently drain the same amount from my CC. I get no oily vapor smells after a hard run.
Either your engine is well-worn (or rings are just not sealing as well as they should) and/or you consistently drive like a bat outta hell and/or your PCV system has a problem. All of which are contributing factors to excess oil consumption.
