...how about combining the basic resource diffusion with some (few and far between) traditional ore veins? Similar to what RSO does?

This way extra technologies for changing the mix won't be needed anymore, as player will be able to find & mine a vein if his factory needs more of a particular resource. Of course, veins shouldn't be too big or too frequent.

Thanks for trying the mod and the suggestion. I did explore a variety of options for resource distribution but was unable to find one that I was totally satisfied with. Ultimately I decided that a uniform distribution of resources everywhere was better than any alternative.

It is not hard to change the mod to get the effect you desire. Get rid of the code "e.destroy()" on line 62 of control.lua, and replace it with

e.amount = 1 + math.floor(e.amount * 0.2)

This will preserve all existing ore veins but reduces their richness by a factor of 5. Then get rid of the research options defined in data.lua.

I haven't yet tried this mod, but I am curious of one thing. If resources mined are completely random, getting too much of some resources could be a problem when they fill the chests in the filtering area. This would lead to belts getting cluttered with excess material that blocks all other material from getting thorough. Could it be possible to prevent miners from collecting unnecessary materials based on circuit or logistic condition?

Also would be very cool if it had mining machines that move by themselves - something like trains with mining equipment on their sides. This would reduce the amount of manual work, but maby it would rather be a mod of its own. :)

The research options provided by the mod allow you to balance the resources you receive. If your filtering area is getting backlogged with too much of some resource, you can research the techs that give you more of the other resources. The techs can be repeated as many times as necessary to get the ratio you need -- but they are expensive, so better in the late game.

There is some manual work but once you hit construction bots it is very easy. If you want less manual work you can increase the richness by editing config.lua.