If by device you mean tinker - no. Only when you get belt/gloves, the item for the craft is from a vendor for less than 2g. You will USE the items 100+ times, many even 1000+ times, for every tinker you put on. Hunters also get scope on weapon, which is a proc rather than an on-use.
A very small %age of them. Pure gold farming is better gold/hour on almost all servers. The sky golems mat cost is mostly in the daily Cd - very little time spent farming over 30 days.How many engineers are crafting armor, guns, and other weapons for sale? How many engineers were farming mats for the Sky Golem in 5.4?
Except it isn't, and you're just proving more than more that you've never raided properly. At this point I'd be amazed if you even ever had a max level engineer, you clearly didn't use it correctly if you did.The point is this; With any profession, you're spending most of the time gathering mats, and crafting items. That isn't what classes spend their time doing. Pressing a 10 second enchant every minute in order to get a boost from Synapse Springs is only a fraction of the time you spent leveling to the profession's max level, gathered the necessary mats to get to that level, and gathered the mats to actually build the springs themselves.