>converted the Topaz video output to PNGs and then touched them up with Irfanview and Premiere
That's a double step, intensive but sounds good, he probably moved contrast to pull detail out of the shadows. I recall watching that movie many years ago back in the old, old place but i almost felt asleep, it is an artsy direction with the purposely high key grainy footage so in that case i don't think he had much trouble.
>I haven't actually watched a full film that's been restored like this
The Gay Porn Acting without the Porn
community has some Topaz 4K conversions and few 8K scene upscales if you really want to see what a normal, standard upscale looks like. Here's screencaps comparing the same scene in the classic wholesome, totally non-gay and definitely not awkward dialogue sequence. Because these flicks had native speeds of 30FPS from the typical digital camcorders the 60FPS conversions are not that jarring, 24FPS can still cut it but in old timey sources that have FPS below the 18 count, like 16, 12 or even 8, the footage starts to look jarring. I haven't seen it but i guess if you apply motion blur the program will overwork and produce, i suppose at best, scenes akin to artsy 90s asian action sequences if original footage had considerable camera movement.
Interpolation software and procedures have greatly advanced in recent years so that quality gap in low FPS footage can be somewhat narrow now if the original camera position was static, but we are still a bit far from decently upscaling low-resolution footage.