[officedweller]

Looks overbearing, so the City will probably require it to be broken up.

The fins add to the monolithic nature when viewed on an angle.
I would prefer dark glass (without fins) to recede into the night sky if office lights are off.
ie use the same glass and detailing as 402 Dunsmuir (without the trendy angled facades) and that would work for me.
That would also contrast with the aluminum fins on the former Sears kitty corner - the proposed fins may be matchy-matchy to the Microsoft / former Sears facade.

Uses and preservation all sound good!

You can see the same design principles at work (to differentiate the old and new) as at the Waterfront Icepick proposal - apart from the fins. I think you can also do the same with dark glass.