Thanks, by description/example in that thread it sounded exactly like what I needed. It installs fine (Tools/ Nyquist Plugin installed followed by Tools/ Plugin manager / Rescan) and shows under Effects / Level Speech 2, but I’m unable to find parameters that work for my use case. It seems I need to lower limiter threshold all the way down to 0.1 so it will amplify low volumes, but then it also have noticeable distortions at normal audio 
Ah, that’s too bad. I was hoping one could automate that with a macro. I guess .ny plugin might be able to iterate over labels and apply effect to each of them, but that sounds like waaay too steep learning curve. Unless someone has simple example that iterates over labels and does something with audio?
Hmmm, I’ve tried playing with it, but unless I crank up degree of leveling up to 5, it does not increase the volume enough, and if I do, it does distort the normal parts too 
. Quick playing with other sliders doesn’t seem to influence result much.
Thanks, I’ve played with that and it seems interesting. Setting compression level to 0.95 does amplify low volume parts almost as much as I would like it, but it also affects the normal volume. But there are so many options in that one that after an hour playing with it I did not reach ideal results, so I’ve given up.
I’ve found other related threads: How to increase volume of portion of audio track? and Raise volume of lower parts without affecting the rest
In the end, I’ve found that running included Compressor with -50dB threshold, -75dB noise floor, 10:1 ratio and make up gain for 0dB checked, produces acceptable results without too noticeable distortion on “normal” parts (might need to run it twice on whole audio for exceptionally big volume differences, or audio tracks that has multiple different levels of “low volume”).
While I’d still prefer a way to automate my workflow as it leaves “normal” audio parts 100% untouched, unless someone has simple example how to iterate over labels, I’ll live with this solution.