the problem with setting it up to miss on all fails is that it will consume a jewel no matter what, like if you click some other item by mistake (one that cant be spellcrafted) or if you try to use a spell creft on the wrong type, like Luck on a shield or such... that's not very fair to players who are just learning the craft.
It was like this in the early versions of Spellcrafting, it was seen as a bug, and fixed.
The best thing for this system in that regard is to have it based off skill, then if your skill check misses (or even if it doesn't), then consume the jewel, and also give it a chance to blow up. That way, a player can get better at crafting and not have it blow up as much later, but in the beginning skill levels, it can blow up most of the time.
and a few other things...
Also, maybe the number of Jewels required could depend on which craft you are adding. Lots of people on my shard use luck, but not mage armor, so mage armor would take maybe 2 jewels where luck would take 5, or something like that.
However, my main concern is setting the resistances and faster casting so they do not stack. This is very very bad as it allows a player to make Godly items.
Plate mail gloves -
All resists 70
ring -
Faster Casting 10
Thats all they will ever need. The faster casting makes mages way too powerful and the resists allow even mages to have full resists on 1 item.
Spellcrafting, if not properly checked, can completely unbalance a shard.
You have to make it hard to do, hard to get jewels and be sure they can't make items too powerful ... but at the same time, you have to be fair to players. It's a juggling act.