I think that iron and copper dust blocks give you iron and copper blocks respectively, I don't see how this could cause any issues.

for gold dust blocks make it so when you smelt the block version you get 20 carat gold ingots since 9 gold dust smelted into each other give you 20 carat gold ingots.

Durability for manual smelters should be 9x so a flint a steel last one stack would lest 9x less when smelting a dust block, in a sf electric one either the energy cost should be 9x or time takes 9x longer.

I feel that these 3 types of dust block are most useful so if you will not implement this for the other types of dust blocks it's understandable.