One thing that I'd quibble with is that I haven't see the value of passive regen going away when you get full epic gear.
None of the following will really matter if you don’t have an adequate amount of spirit for passive combat mana regeneration. While you may have to stack some spirit at lower gear levels (346ish iLvl), once you start getting some purple pixels this will become less important as your gear will provide more than enough.
What is happening with the Straw Hat Pirates is that as we get more gear, I don't have regen issues on the on-farm bosses, but we immediately go to work on more difficult bosses where there's a lot of healing. On progression bosses, I still find mana to be a significant concern.
I frequently run into druids who think of regen as something to get enough of and then you stop. This point of view is only helpful if you have a set number of raid bosses you will ever attempt and then stop. For the most part, I don't think it's very helpful to optimize for on-farm bosses. In theory, you can optimize for repeatability, but once you start out-gearing an encounter it's going to be pretty repeatable no matter what you do.
Given the small percentage of guilds that have Sinestra down, there are precious few of us who are likely to hit the end of progression before the next raiding tier comes out.