"when f/4 is too slow, you will curse the gods and the high heavens and start weeping uncontrollably"
Eric, you are killing me! It's true the 70-200 is almost never used indoors, so not sure how much I'd miss that stop. I don't have a feel for much I'd miss the shallow 2.8 DOF.
In general my philosophy (with cars, cameras, lenses, mutual funds) is don't sell, just use it until it's dust. So I am always 'scared' to sell something perfectly good, like the 70-200 f2.8, which I've enjoyed. I'm still leaning toward get it from KEH, try it out for two weeks, then decide.
Before I had the Nikon 17-55 I had a Sigma or Tamron version (this is mabe 5 years ago). I hated it so I since then I have tried to stay with Nikkors, though I enjoy the Tokina 11-16 and the Sigma 30 1.4, although the focus is not 'zippy' on either one. I"ll do some reading on the Sigma and Tamron 17-50's.