hmmm... SPI is certainly great for a very late game, when turns of Anarchy keep on getting longer and longer and you have to stay flexible in a very tight victory race.
I don't mind playing actively, and I do that all the time. In a forum, we just outline general ideas and convictions, but in reality they go to hell quite often.
But I feel the exact opposite, being SPI is a passive thing for me because you can switch whenever you think it will benefit you. Being not SPI on the other hand requires good planning of civic switches (double switch, golden age...) and that can be done without bigger harm.
Well, I am also ready to learn. What is so great about SPI, a trait, that comes into play only 7-8 times during the whole game? (okay, and the temples). Does it really hurt so much when you are in anarchy 10 turns out of 500? There must be something about it, because Mansa is such a strong AI leader. Hatchy, Gandhi, Isabella are also strong in many games. But except Mansa, all these guys found at least one early religion, and then you can really leverage the SPI trait. The human player on the other hand avoids religion for quite a while & does not build temples before AP. I see that SPI in the hand of an AI can be good.
My impression is, when someone plays a SPI leader on video, he purposely switches in and out all the time just to show what is possible. But is it really needed. I mean, when an AI asks you to adopt civic XY, would you do that even if you don't want that civic? In a normal game, the answer is probably no. Being SPI, you can do that and switch back, but it is very unlikely that the little boost to the relationship will decide the game.
Same for religion. Switching religion just for one trade, well... this is a very theoretical construct that one could belief after too many of Lain's video introductions. In my understanding, a religion has other purposes. Either it benefits you directly (then you adopt the religion that is present in the most relevant cities) or it keeps the crowd resp. a dangerous warmonger happy (then you want to adopt their/his religion. Also, in a GA, you can rethink your decision and adapt to the a new situation. I have really played and seen many games, where staying in the same religion throughout the whole game was perfectly fine and brought all the benefits that you can expect from a religion. And to please someone short-term is also very short-sighted. Maybe in that same turn, the warmonger on your borders drops to cautious and starts plotting on you.
A completely different approach to that: On IMM, it is not unusual to build that wonder for 12T-Golden Ages (Mausallos?) when you have marble and that can replace quite decently SPI trait (of course only partly). You make your first switch in the beginning of a GA, you can use that for quite a while and in the 12th turn you switch again. In at least 5 of my games, this has really boosted a lot. So staying 12T in caste + pacif. in order to produce some GP guys and then switch out again because you got what you need and the civics do not serve you for the moment.