> The value of an attention span is non zero, but if the speed of access to information is close to zero, how do these relate?

Gell-Mann Amnesia. Attention span limits the amount information of information we can process and with attention spans decreasing, increases to information flow stop having a positive effect. People simply forget what they started with even if that contradicts previous information.

> If I can solve two problems in a near constant time that is a few hours, what is the value of solving the problem which takes days to reason through?

You don't end up solving the problem in near constant time, you end up applying the last suggested solution. There's a difference.