As for the reason why the invasion wasn't in the Japanese options.
I think zraver makes very valids points when signaling the IJA vs the IJN respective influence, and the fact that a Japan who thought it was the center of the world couldn't bring itself to realize how important was its conflict vs the US. Much more so than anything that happened in what they considered their backwater: China.
Anyway, I suppose to know for sure one would have to unearth the IJN deliberations records to see if it was in the cards at some point. I've been thinking about this issue in the last hours (and frankly, I'm a bit saturated with having LOCs and shiping lanes across the Pacific in my mind, which I don't really understand to start with).
It has occurred to me that maybe another factor was that the Japanese simply didn't realize what they had within their reach. Specifically, the devastating effect of a surprise attack on airfields, and the resulting air superiority they would have enjoyed; so if I'm not wrong that might be one of the reasons they didn't even contemplate an invasion. They copied Taranto too literally. They assumed the air fight would not be settled in their favor and an invasion was impossible, my bet is that they didn't even think about it, when in fact it seems very much doable.
As I don't have access to the Japanese IJN archives, and anyway, I don't read Japanese, I suppose I'll never know for sure. I can live with that, the only drawback being everytime I try to watch the 3 hour long "Tora, Tora, Tora!" I'll be unable to concentrate in the action, and would instead entertain grandiose plans of conquest across the Pacific .