True, been around for a while, when steemit was the main platform :)
I like automation and Python, and loved your detailed info on how you made it work, helped me out a lot.
I can't recall why exactly, but I guess it's all about optimization. It's the API url that peakmonsters use, and has been working well since a few months ago. Can't find it in the official changelog though.
sm_update_rental_price is documented here. Not sure when it was implemented, but I guess it was with the new rental system came to place? The advantage is that you don't have to send more than one transaction with all the updates, instead of cancelling and publishing. Also, I don't think the transaction type used in the OP is working any more.
I considered making a call for the API for_rent_grouped, but as you can't call for a specific card ID you have to pull the entire list for all ten market levels. May save some though, as per card data is pretty much as well. You just have to keep track on if your current listprice is the same so you don't underbid yourself.