I was a little hesitant at first, but now, after doing it and seeing the IMMEDIATE benefit and the ease of doing it, I wouldn't even think about going back to the old valve. What a POS.
Could easily be made to look better for smog inspection. And a few of the cans look OEM. See the one on the OP of the thread I used as my guide. With 3/4 hose from start to finish it can easily be made to look like it belongs there. In my state, we don't have smog checks or even state inspections so I didn't worry about how it looked. This was more for proof of concept. Eventually I'll get a better can with 3/4 fittings so I don't have to neck it down.
Considering I have roughly $30 invested in this setup, so no a rebuild isn't even in the same stratosphere in relation to the cost.
Even when I get my new engine, I would run this vs the stock setup. The M54 is built with LOW tension piston rings. Extra vacuum helps them seal, this makes the car run better, plain and simple. A guy I know makes scavenge pumps for race prepped E46's and other BMW's and says that they usually see 15% increase in power on the dyno from extra vacuum. I can also confirm, you will feel it. Or at least I did.
It also is a much cleaner way to run your vehicle. If you look in the post I linked on post #1 you will see on page 6 or 7 that the original guy who did this cleaned his tailpipe of carbon after doing the mod. He had NO carbon residue to speak of after many, many miles. I would bet that nasty black residue we all get inside the intake (you see it when you replace the DISA) will be greatly reduced if not eliminated this way. And because it is still a closed system it is emissions friendly. I have been running it for 2000 miles and have gotten NO check engine lights and all my trims look spot on. The guy who gave me the idea has over 30k miles on his setup if memory serves. No issues.