Not everything is useless.
Gold is still some what useful as some of the stuff cost a lot of gold (like Enchanting). Some Legendaries will still remain some usefulness like Mempo or Inna's pants as long as you have godly rolls on everything except main stats which you can roll. Hell I would even say that Amulets/Rings from old D3 are good too if they have trifecta plus main stat because you can just re-roll the main stat.
Not sure if they will keep that stuff though ie. re-rolling legacy items or even let you carry over stuff but this is the trend that is followning in RoS.
Stuff that is definitely going to be useless in RoS:
*Gems (you get Marquise gem at the same drop rate as Flawless Squares)
*Weapons
*All crafting materials
Stuff that has retained some value:
*Pure DPS gear that only needs the main stat rolled
*Some Legendaries that rely solely on pure DPS stats (like Mempo, Inna, Witching Hour) which you can roll the main stat on
*Gold
http://diablo.incgamers.com/blog/comments/diablo-3-to-reaper-of-souls-item-upgrade-guide#more-373399
Here's a link you can read more on.
Most of this stuff will change and apparently Blizzard is saying that they will implement a change where you can upgrade your current crafting material to RoS level stuff (so basically 10 Brimstones for 1 RoS legendary mat). If that's the case then I would say its worth keeping your crafting materials.