Yeah this has been common sense to me, but I've always farmed the mats instead
Tried this yesterday, with buying the ores (had a shitload of eternals in bank) and prospected em. Spent 600g on saronite ore and now after prospecting and crafting the rares I got into gems, I already made over 900g. And I got like 200 JC crafted rings/necks waiting on my bankchar to be dissed. So, VERY profitable.