I don't necessarily disagree
I don't necessarily disagree with you. Since it helps if we both use the same numbers, I'll just use yours without verifying them.
If the average lifetime is 160k miles, that is the expected lifetime until the first cell failure. Generally nimh cells last 500-100 charges. That's a large window. Considering that the Prius battery has many cells (168 total in 28 groups of 6) you're likely to get your first failed cell early in the failure window. So that 160k miles is likely the beginning of the typical failure window, placing the upper somewhere nearer 300k miles.
This leads me to conclude that it makes sense to replace the first few cells. I'll probably repair 3 failed cells (replaceable in groups of 6) before replacing the pack due to the failure window.
Alternately you could replace each of the individual batteries in the pack, likely for less than a full replacement pack.
I'll probably replace my entire car right around 220k miles, since the car will likely be worth less than the replacement cost.