It never hurts having some spare memory onhand. When the new build comes about you will likely be running DDR3 however being an upgrade. If you end up buying a new case then these will be ok right where they are since the new build will be totally fresh with a new case, board, likely newer video card while you may decide to move the drives you have now as well as the supply into that one.
You wouldn't want to put in any case you want to be a modded show case for sure.
