I think everyone knows that Gold, Silver and Bronze are not really used by most of the Players, here are some examples:
Bronze: Crafting of Advanced Alloy and no other good use, except you have Forestry-Mod.
Silver: Only Glassfibrecables and for actually nearby useless RP-Stuff.
Gold: Nothing except decoration or golden Apples.
Yes, there are Armors and Tools but with Nanosuit, Quantumsuit and Electric Tools they are useless.
I suggest some minor changes and additions to make them a bit more usefull:
Bronzeusage in the Pistonrecipe.
Silver instead of Redstone for doubling the output of the normal Circuitrecipe (like with Glassfibrecables).
Silver and Gold instead of Refined Iron for ICredits.
Gold used in the recipe of Advanced Circuits.
With these minor changes are these Materials more used as before.
Something more timeconsuming would be a Bronzemachineblock.
With it you can craft, less fast working, Bronzemachines to safe your Iron. It's only possible to craft basic machines with Bronze, like: Macerator, Canningmachine, Extractor, Compressor, Recycler (crafted out of Bronzecompressor) and the electric Furnace. These machines are not upgradeable and therefor they are having no slots for Upgrades. You can also craft a Generator out of Bronze, which is only upgradeable to one Watergenerator or a less stable Bronze-Windgenerator, which breaks faster.
So, that was another Suggestion by me.