[pandaman]

>What smartness in modern TVs can I get that's important to me that I can't get via a Roku or similar device?

Only you know what is important to you, but I like automatic volume levels, for example. I stayed at AirBnB a couple years ago, which had some commodity TV (Vizio?) w/o automatic volume and learned they still do loud commercials. My home TV keeps volume at the same audible level during commercials. Same with auto-brightness, I get nice image all through the day and night illumination levels in the living room. Voice control is handy when you don't live alone so other people may have a remote at the moment or it could take some time to find.

Apps on my 6 y.o. TV still work just fine, I don't need to attach devices to a TV, which neatly hangs on a wall without things hanging from it. The TV is running Android so it will keep updating from the Google's app store as long as the app vendor keeps maintaining it.

[BeetleB]

Of these, the only thing I would like is automatic volume control, and HW only versions have existed for a long time.

Auto-brightness - I put in a lot of effort in setting the brightness/contrast, and would really not want some SW messing it up.

Voice control - couldn't care less (and yes, I do own voice assistants and use them).

[pandaman]

Something claiming to be X doesn't mean it's X at all least good at being X. This option on tube TVs that I had never worked for commercials, works so well that I don't notice it on a "smart" TV.

If you don't want auto-brigntness you don't have to enable it. I have a hunch that a TV sets it better (just for the reason that you are unlikely to adjust every time you turn lights on and off) but tastes do differ indeed.