I am not a JC but i have friends that are, but I am a miner.
Prospectng in general is hit or miss, from what i found from my friends its pretty random and not reliable, generally speaking the jewels they got were used to craft with and not to sell.
From this i understand it to be that ore will sell more in general as multiple professions use it. The profit (wich there isnt much of due to supply/demand) from JC is selling finished products. And since there are a TON!! of JCs out there now theres not much profit to be made.
As i said I am not a JC, but from friends and what i see on the AH day to day, you'd be better off just selling ores than trying to sell finished products, especially now with so many JCs. In a few months this may change a little as the interest will die down.
As for selling mining mats, the prices are great, i make good money each day from the ores i sell on the AH wich is making it one of my favorite gathering profs ATM.
IMO crafting in general is a waste of money, on all my toons i use 2 gathering (general skin/mine with a few skin/herb) and one enchanter for DE purposes. I make good money this way and apart from sending my new alts a couple nice bags they all have more than enough money to buy whatever there little hearts desire.