If mineral generation [is] effected everywhere then it wouldn't be unbalanced.
Except it's also random everywhere. There's no guarantee anyone's home system will have a gas giant with millions of tons of Sorium, and the difference between having one and
not having one is huge.
If you have plenty of minerals in your starting system then so does the other guy and the difference would be who expands more quickly.
Difficulty would remain the same but you'd have more of a margin of error to do new things, experiment, and fail which is important in a game like this.
Except you are not guaranteed 'plenty of minerals' -- and the possibilty of a superabundance of one or two has massive implications for expansion. C# Aurora now features NPR AI with the philosophy of "explore everywhere, as fast as practicable"
and "only explore new systems when one or more minerals run low."
I would counter that your margin for error is overshadowed by randomness. The problem is akin to the folks who insisted that wealth generation was easy & limitelss and building Infrastructure was foolish. . . because they always played Sol starts and colonized Luna and subsidized shipping lines and sat back and watched the money roll in and the free Infrastructure materialize by the thousand. Those of us playing conventional starts in random systems had a very different experience.
I am very concerned that any 'universal mineral abundance modifier' would have significant -- possibly catastrophic -- effects on NPR AI & behaviour. Remember the VB Aurora 'difficulty modifier' for NPRs.