I am too early in this time to have too many benefits in the breathing department, I smoked for 33 years pretty heavily for a lot of those years, but I am breathing a little better already. I can smell better and my nose isn't nearly as stuffy as it usually is. I don't get migraines as much either.
At this point I may never have a great set of lungs, but vaping will give me back what quality I can get. So in my estimation I don't need my Doctor to tell me it's OK or not OK. I only need to listen to my own body.
Actually, LeftofCenter, you're in luck! Once you stop smoking, the lungs begin to heal all by themselves. It can take a while depending on the damage, but they repair that damage naturally over time. When I was smoking I could barely walk a block or two before having to stop and catch my breath, and taking a deep breath *always* made me cough, sometimes painfully. But I was breathing better within a few months of vaping, and now that it's been a year off the cigs my lungs feel wonderful. No more pain or coughing, and no more bronchitis.
So hang in there, man. You're going to love having your lungs back =)