A couple of miscellaneous responses to this thread:
171 cabs are quite wide and spacious but they also have their downsides. They do not have power sockets like the newer 377s (and I presume 387s). The emergency stop buttons and GSM-R red buttons are in quite awkward places which are reasonably easy to knock if you are on a wobbly bit of track (see also: the Cowden area!). And the desk on the second-man's side is sloped a bit awkwardly and is too high for you to rest paperwork on whilst sitting down. Several of these things could be addressed by a cab rebuild to make them similar to a 377/6 onwards, but not all.
As for 377 cabs making people strangely sleepy, I've somehow always attributed that to not just the dark central section where the gangway equipment is, but also to the air con. I may be wrong, though.
Regarding the ex-Scotrail ex-170s, obviously they are being reformed and I believe the interior is meant to look pretty similar to the existing 171s, so both of those jobs are fairly large without considering what's below the sole bar. I should imagine the Door Deselect system will need pretty decent testing to ensure that it all works well on reformed units. What I have heard is that some of the electrical equipment is in a bit of a bad way and needs at the very least some repairs, and I believe this is engine related, but I do not know any further details at all. I could be wrong here, but that's just hearsay for you, really!
I would expect that many of the units will see approximately similar use if they are simply being added to current services. And, as posted on here somewhere before, remember that many of the 171 consists do at least two peak-time return journeys in each peak, so they are not just doing one trip to London and back each day. It would be lovely if units could be stabled in the Uckfield area as I have a feeling that could help reduce mileage and costs, somehow. But I don't think that's going to happen!