For example, pretend you have three square amethysts, two tomes of jewelcrafting, and 20000 bucks. You want a flawless square amethyst. How should you get it?
- Go to the jeweler and hit a button. You lose all the previous stuff but get a flawless square amethyst.
- Put all that stuff for sale on the auction house and buy the gem from the auction house.
- Vendor all that junk and buy the gem from the auction house.
- Leave all that garbage on the ground and buy the gem from the auction house.
To start, the vendor value of three square amethysts is 138 bucks. Two tomes of jewelcrafting are worth 86 bucks. Right off the bat I'm going to say it isn't worth picking them up if your plan is to vendor them. To answer the rest of the question we need to know the auction house values of the various goods. The game has only been out a few days so I doubt these values are stable but for now we have:
Square amethyst: 4000
Flawless square amethyst: 14500
Tome of jewelcrafting: 1000
Right off the hop we're better off leaving everything on the ground and buying the flawless square for 14500 instead of spending the 20000 combine fee. Even if there was no combine fee, however, we'd barely be breaking even using the crafter since the material cost is 14000! The AH does take a 15% cut so with no combine fee we would prefer to use the crafter but as it currently stands it's just plain stupid to use the jeweler for this recipe.
I went ahead and built a spreadsheet with the values for all gems up to flawless square. (There are no perfect squares or better for any type on the AH.) Rubies across the board are worth more than the cash fee of the combines and nothing else is at any tier. Rubies are not worth combining once you take into account the value of the three previous gems.
As I said earlier, these are initial values. The thing is, I can't see the values of these gems rising over time. More and more gems will get added to the game and none are ever removed (except possibly by crushing them together at the jeweler) so the values should drop. And since the values right now are lower than the combine fees it's pretty incomprehensible that it'll ever be worth using the jeweler at these tiers. I honestly wouldn't be surprised if Blizzard ended up drastically lowering the combine costs to encourage people to use the jeweler at some point.
As things currently stand I am not going to bother looting gems on my alts. Maybe I'll pick up perfect rubies or better with the intention of using AH slots trying to sell them...