Miniaturization aka Nano-technology & Resource Optimaization

I think what you'd have to do is put a Get_Empire_Tech_Level call into the tonnage field of your components/facilities/whatever that you want to miniaturize.
So if you wanted it to be 2% of the original size lopped off every level, use this formula (assuming 40 is the original tonnage):
40 - (Get_Empire_Tech_Level("Miniaturization") * 40 * 0.02)

Or if you want it to be exponential (2% off the first level, 2% off of the already-reduced amount the 2nd level, etc.) use this formula:
40 * (0.98 ^ Get_Empire_Tech_Level("Miniaturization"))

For the cargo storage, I think you can use the ability used by the Advanced Storage Techniques racial trait (forget what the ability's called). That ability is supposed to increase cargo storage by a certain percentage; if you attached it to a "cultural achievement" sort of thing then that should do the trick.

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The power of the ancients is now yours to command. You are truly the Master... of the obvious

'^' would be to the 'power of' as in it will be 0.98 multiplied by itself 'tech level' times. As in tech level one will be tonnage*0.98, level 2 will be tonnage*0.98*0.98, level 3 - tonnage*0.98*0.98*0.98, etc. I would think that the first option would be the easiest, the only problem being if you have too many tech levels the components could get very small. I hope this made sense.

By default, SE:V will usually truncate decimals.

Space Empires Depot | SE:V Balance Mod

Hmm... JinXXX, if you want to make an empire-wide ability, you could try this... I don't know if it will work (Malfador's implementation of applying abilities to places where they're not used in stock is a bit spotty ) but here goes nothing:

The ComponentEnhancements.txt file uses an ability called "Component - Tonnage Space Taken Percent" to increase the size of mounted weapons. If you were to place that ability in a cultural achievement with a negative value, it MIGHT reduce the size of all components when you gain that cultural achievement.

I doubt there's an ability to modify facility tonnage, though, but this could save you some work with the components at least

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The power of the ancients is now yours to command. You are truly the Master... of the obvious

I don't think % bonuses stack like that (10% + 10% = 20%)...my understanding is that they're applied one at a time, so say you generate 100 points plus 10%, that's 110, plus a further 10%, bringing you up to 121 (correct me if I'm wrong, it's a little after three am, I don't expect much of my math skills).

Anyways, it works out to 21% in my example if that is the case. Not much of an increase, but still noticeable, especially when you hit larger numbers.