The system assumes a certain degree of transparency to function as written. You don't know if you need to spend fate points unless you know whether you succeeded or not, and they're too precious to throw onto rolls when you don't know whether you need to.

You could work out some system whereby you say something like, "You're not quite making it up the fence..." and let them spend the fate point. But then you're just putting success and failure into code, and you have to rely on them interpreting the code correctly to make their decisions. This is just a layer of obfuscation on top of the system information. And it's not a layer that particularly reduces the game-ness of the game.

There's already the system of adjectives. Fudge was originally designed so that you don't need to speak in terms of the numbers. You can say, "It's fairly difficult to climb that fence," or, "It would require someone with a good degree of skill to pick that lock." Because characters would have a general perception of how hard something seems to be while they're doing it, and that can translate directly to mechanical information without interrupting narrative flow.

But ultimately your group needs to work out what everyone is comfortable with. FATE does make some assumptions about what range you fall into on certain topics, so you might need to nudge it a bit if you find the assumptions don't fit in the comfort range of your group.

I think that because of the Fate Point economy, it's important for the players to know the total difficulty necessary for a roll to succeed, so they know whether or not to spend a FP. Because bad things have to happen to your character in order to get FP, making a player spend one in a situation it's not important to do so in seems excessively cruel to me.

But it isn't free form enough to make up your own spells is it?

There will be a solid date when we have a solid date. But we won't claim we have a solid date before we have one.

Great opportunity for a little DFRPG Beta testing