Steeper hills, in terms of both form and and training benefits, probably mimic/impact acceleration more than top speed. As far as 400/800 training, KitKat included lots of 300m shallow hills as a sort of ‘overtime’ as opposed to ‘overdistance’ in his 400m training for his athletes.
Matt’s commments on stairs and front side mechanics interests me. My son (not a sprinter) often seems to shorten his stride (looks choppy) even when he should be at full speed. I think it is a problem with front side mechanics and knee lift (not stepping over). I’m wondering if stairs would help or aggravate that tendeny.