On top of this, as a heavy vi user, the main navigation keys are no longer on the home row for either Colemak or Dvorak, which means I either need to make my editing far less efficient, or remap nearly every key.
I have had many very intelligent people attempt to explain the switch to Dvorak to me, and never heard a good reason to invest the time. I am curious if folks invested the same amount of concentrated time improving their QWERTY skills (relative to the amount of time folks spend learning a new layout) if there would be a similar speed improvement.
It's sort of like the much-talked-about switch to reverse scrolling in OS X. You may think it's a big deal, but your brain makes the adjustment, and it just doesn't matter. Your vi editing efficiency should be pretty nearly unaffected. It might be very fractionally slower, since the navigation keys aren't on the home row, but .. I never notice it at all. It's definitely not far less efficient.
Not arguing that you should switch, incidentally. I could also touch type 100+ wpm on QWERTY. I never regained my original speed after switching. That's very common for very fast typists. If you don't put systematic effort into speed training, you'll lose some speed for switching. Not that it's that big of a deal.
I literally never had the thought, "If only I could type faster, I could get this done more quickly..."
I think few slow typists would have had that literal thought either. I know I never did as I approached up to my ceiling of about 70wpm.
If you're a heavy vi user, it's probably not worth it, but if you weren't and you did a lot of typing it might be worth it to see if it helps with comfort. Also, what's wrong with the fun of trying new things?
I sometimes consider changing layouts but it all comes back to that one simple statement. I don't touch type and I still hit the 120 WPM sweetspot on QWERTY - but I feel that any benefit of Dvorak/Colemak would be wasted if I didn't also learn to touch type.
I fear it would be a lot of work for no discernible benefit other than geek cred.