I also have a smart TV that I have never connected to the internet, and I never foresee a reason to either. When I want to use apps on my TV, I use a separate streaming box. If in the future there is a software update for the TV with a cool feature I want (unlikely), I would connect it via ethernet temporarily, perform the update, and then disconnect ethernet.
I would never connect it over WiFi for fear that it wouldn't forget the network. If someone has a smart TV that only supports WiFi, then I would suggest they setup a new WiFi network, temporarily connect the TV to perform the software update, and then disable the WiFi network.