well... i wouldnt say its a goldmine for all enchanters because prices on servers varies depending on how good the WoW economy is. On one of the older servers, small radiant shards are worth like 2g or even less. And clearly, if you buy a wolfhead helm for 7g and then resell the shard for 2g, you'll be losing a bit more than 5g.
Also, running SFK is not a very great way to get money. Still, lets count how long each sfk run it takes. It takes about 30 minutes on my rogue to run through it once. An hour of running sfk is not as good as my rogue grinding in the outlands, especially with the herbs, the drops, and other factors. Each uncommon that drops is at least 10g by then, plus the vendor trash, and such.
Gotta keep in mind how long sfk runs are, because clearly if it takes 1-2 hours to run sfk, not worth it, just go grind and level up. Higher levels get better loot and more money off drops.