Are you going to be doing PvP? Theres a bop trinket (Glimmering Mithril Insignia) that gives a 30 seconds fear immunity only available from a blacksmithing quest chain. Engineers had a few BoP PvP and PvE items as well. If you have a druid tank you'll want to be enchanting for the trinket.

I have no idea though if back in classic you had to keep the profession to use the item. You may have to level a couple professions to max on each toon for the trinkets you need than swap to engineering for the gadgets.