Personally, I don't see any value in a full day dedicated to speed work.
However, I do try to accelerate all my reps forcefully. So as I am working up to my training max and work sets for the day I am effectively getting in speed work by always using compensatory acceleration.
I do see value in speed work if you are having an off day but still want to get in some training.
James 1:16-17 ESV
Do not be deceived, my beloved brothers. Every good gift and every perfect gift is from above, coming down from the Father of lights
With God's help...Mens sana in corpore sano