Great share with some great detail! So many twists that can be done with this. As you mentioned the Pinterest section is definitely light and under used around here so I hope this thread inspires others to do share their own methods and experiences with this method. The issues with the work intensive posting and risks involved with the TOS of adsense are the risks one has to put up with for using methods like this, but as the OP has pointed out the rewards can easily outweigh the risks as long as you are smart. Things like this can have a shorter longevity than other methods so its a case of making hay while the sun shines and making as much as you can when using other peoples group boards. Obviously the risks are higher of getting reported or a site making changes to close any loop holes or make methods harder when posting on other peoples group boards because the owners may get disgruntled and report stuff. The more reports Pinterest get about a topic the more likely they are to act. I noticed the kind of posts the OP showed in the example account a LOT over the last 6 months and recently more and more group board owners are closing open invites or proactively deleting members that do this and the spam that was posted. It's a good job you have a lot of your own boards that you have built up for this method as I'm sure that gives you a lot more control and you dont have to worry about losing them or being removed from them. But if people are smart, dont go overboard and post better quality posts then they should be able to get a lot out of this.
There will always be people doing methods like this with mass posting to social media platforms and I think the key to success is finding the right balance as to not get flagged. I either see people doing it way too much with really crappy quality spam or being far too conservative. OP you have been doing this for a few years now so I'm sure you have found a nice balance but do you think you will you be scaling it anymore with other accounts? Have you noticed any problems with any of your accounts or posts going out with recent changes? Do you do everything manually or is there some scope for automation? I see a lot of people opting for manual over bots to avoid their accounts being flagged in some way, do you think this is the case with Pinterest?