Yeah, I've noticed this as well, and I don't feel anywhere near as sluggish during the day.
I guess the main thing is not ingesting carbon monoxide in anywhere near the same amounts, but it has also to be beneficial not taking in formaldehyde, benzene and all the rest of the crap the lurks in ciggy smoke.
As it happens, my doctor's surgery rang me last week to check my smoking status. I explained I had switched to vaping, and received the response "Great, well done, we'll change your status to non smoker then!" After the best part of 50 years smoking, never thought I'd hear those words!!