One big difference is that Vim has been a de facto standard for a very long time, and it's ubiquitous - you can trust just about any server to have vim installed - so the investment to learn it has a much more guaranteed pay-off.
I'm really into improving efficiency and I enjoy teaching people how to use vi. The class materials are publicly available and are based on Bill Joy's original paper introducing vi:
There is rarely any point learning vi if you are only ever going to use vim. (On many systems, vi is just a symlink to vim anyway).
If I had a nickel for every time someone justified not using vim's features by invoking a bizarre imaginary scenario where they were using vi to twiddle bits on a downed snowflake machine, I could buy a few fancy coffees.
