I was a 1-1.5 pack/day smoker for 20 years. Started off with 18-24mg nic, and within 3 weeks was down to 6-12mg. Nowadays, I actually use nic content more like a juice booster. It has A LOT to do with throat hit and the sting for my palette.
So, I have liquids ranging from 0 to 18mg (sometimes in the same flavor), and tend to just chose what mood dictates. Sometimes nicotine adds a peppery taste, sometimes some spiciness, all depends on what vendor is choosing and quality of the ingredient. But it definitely brings variety to the same flavor, sometimes making it way better!!
The actual physical dependance on nic level for me is negligible. In the mornings I tend to do 0mg, and 6mg throughout the day. When I'm craving a sting or have a particular juice that works really well with higher mg, i just go for it.