I feel like polling twice a day (with the right etags) will beat exponential back offs.

Exponential back off is great for a lot of problems, but irregularly updated blogs doesn’t seem like one of them.

Thinking about it, it's not an easy problem to define because it's got a tradeoff. Getting the content quickly (easy: poll in a loop) vs not using server resources (easy: never poll). We have to define "better" before we can decide which solution is better.