I actually vape 18 and on occasion 24, which to me is harsh.
Sweet spot is 16 to 18mg. 24 will basically (for me) get me too rushed, and I smoked Camels and then American spirits, 2 1/2 packs a day. I still smoke but far far less, and mainly because I enjoy it. I smoke 1 pack of very light tar/nic/co2 cigs, and am working it down and then out. Some quit immediately and some take a little time. I'm down by 80% of the levels I once was, and am on the way out. It's no longer an addiction issue for me, since e-cigs meet and exceed that. This is not a race. It's a process.
There are some who kick the nic level up a slight bit over their cigarette level for a period of time, (say a few months to 6 months) , and then I advise they bring it back down to where they were. **It works fabulously for them and our success rate was above that of the professed percentages in the industry and all polls on the subject**. It was due to personal interaction that can't easily be done on an internet sales site.
So NO, I'm not out to scare or chase people off e-cigs. Just the opposite. But what I won't do is just throw product out to make sales. I want to see successes and long term customers who are informed and aware of what they are vaping.
Since a high percentage of smokers are addicted, it makes you ask, why would you want to push the limits and make that addiction worse by kicking nic levels above where you were originally, unless temporary? Some have a desire to eventually wean off the nicotine and e-cigs, and cut to 0mg over time, and then out. That's an individual choice. Why make that effort harder (if they so choose).
Nicotine has many benefits in aspects of brain health /etc, but it also has a few down sides. One is it's a vascular constrictor. To push limits in that regard is unproven but most doctors will tell you that's not a positive.
What is a positive is getting off of cigs and the many issues they cause.
Always keep in mind, the whole E-cig concept is NOT "Harm Elimination", it is "Harm Reduction" and to an unknown degree, but the info I read is it's 100-1400x safer than cigs (and much depends on factors like how much and what you smoke(d) and what you vape). Fabulous positives.
Flavorings are the weak point of any e-liquid. Some even have a tendency to burn. Same with some cartomizer battings and wicks (all of this is a side issue to this conversation)
Nicotine is also the addictive agent, and you know that. Why up the levels if you know that, except for the short term purpose of getting clean of cigs? This is not the search for the ultimate "High" . This is meeting and slightly exceeding where you are and combating cigs.
I believe in informed customers who are out to get clean and not hurt themselves in the process, even if it's a temporary issue like headaches/ jitters/nausea/etc..
I ran into many who had issues with the higher levels of nic, as well as those who had flavoring allergies and a few with PG allergies. We're talking some scared and shook up people who wanted in the worst way to keep vaping instead of going back to cigs. It makes sense to get them balanced right, but I won't tell someone that ANY level of nicotine is safe. We have our tolerances as individuals, and there is a common sense limit. Many cannot handle high levels of nic, and to make a blind statement that 36mg is safe is irresponsible and very individualized. Most cant handle it, and the polls show that (19% only are going there).