Sure, smoking does make you more susceptible to colds and flus- that's just some basic knowledge right there. I don't think there's much evidence it has to do with Vitamin C though (feel free to provide a cite and educate me on this subject though.) Smoking does have a pretty bad effect on your cilia, and those cilia perform a number of important functions. Some of them help prevent colds and flus, so it's not surprising that smoking makes you more susceptible.
So let me get this straight... you dismiss quite a lot of anecdotal reports of less colds and flus from vapers out of hand, but then report an anecdote involving one subject (your wife) sniffing lavender? I'm less than convinced.
I'm not that interested in the incidence of colds though, tbh. I am very interested in the diseases that catch up with us, if nothing else does. Alzheimer's is a terrifying disease. I've known a few people who had it, and to be perfectly honest if I were diagnosed with it I'd take myself out to the backyard on a nice sunny afternoon and end things while I had the chance to go out with some dignity.
It turns out that smokers are less likely to develop Alzheimer's than non-smokers. We don't know why that's the case, but it's interesting to note that nicotine is structurally similar to acetylcholine, a brain chemical that declines in Alzheimer's patients. Further study is needed, but there are reasons to believe that nicotine might help prevent Alzheimer's.
Further, nicotine makes you more alert, more focussed, and in large doses more relaxed. I'm inclined to call that "better health," though I know that's controversial.
