This is interesting. I found watching other vapers progression is that I think it arises out of boredom. Either with gear or with Eliquid, or technique. When I smoked the only thing I changed up was a switch from pink disposable lighters to purple ones. Shrug. With vaping gear its different, you can match your mood, or your shoes, or the level of disposable income you have now that you didn't have as a smoker. You can satisfy your own nature for change.
I am still using the same type of gear but I do change out the colours every week. Why, because I can and it keeps it interesting.