all icons are 32x32px but they have to be 64x64px (for people playing on high settings).

well, I guess I m wrong. but mod didn't load by telling graphics are not 64px, but I resized them and it did load. but now I can only see 1/4 of the icon ingame (top left coner).

Seems like this is not ur issue.
I sorted out that it's an incompatibility with https://mods.factorio.com/mods/Doomquill/research-queue
which doesn't support 32px images.

I might add HD graphics some time, but as you say, I don't think it will cause any major problems if I don't (other than compatability problems with mods expecting HD graphics), so I'll leave it as it is for now