Engineering gives a Paladin additional tools or tricks that can be used to complement tanking and pvp. Most of these items require engineering to use.
Jewelcrafting, yes you can make some trinkets that would help you out, but a majority of items can be bought from other jewelcrafters or the AH.
Enchanting is great to have. The soulbound quest rewards that you just sell can instead be disenchanted for materials. However once again you can have someone else enchant things for you. You don't have to be an enchanter to have them.