I think you are giving the skill a whole lot more power than it has as written Saeviomagy and that may be where part of the problem is coming from.
still though, I know there is a slight cost disparity, but which would you rather have as a character: a +6 dex item or +15 sleight of hand?
If you give it that much power I can see why you would go for the second, it would be the uber skill from the great beyond. If you cut down its power to a more reasonable level (reasonable in this case is just my opinion of course..lol) then the first would be much better.
This strikes me as similar to the thread about diplomacy and someone saying that with a +30 you can make someone your best friend in the world who will then stop fighting you and give you all of their stuff. It doesnt do that, nor does slieght of hand, in my eyes, allow you to do some of the crazy powerful things you listed (stealing someones rings off of their fingers? not going to happen while they are still alive except in the rarest of circumstances).
So yes, I definately see, 'lifting a small object from a person' as taking small objects from them that are not specifically tied up or down somehow and not in hand. Being able to take things out of peoples hands would make it much better than disarm, taking off rings would be well into epic.
Also, the dm limits the number of free actions in a round. While technically you could do it a large number of times I doubt limiting it to one free action per round for this would be too bad. It still does exactly what the feat should do, but keeps it from going overboard. I suppose an extra attempt each round could be attempted with an extra penalty of 10 for each additional one. (That way, with a big enough bonus you could get several items in a round).
In any event however, sleight of hand is a pretty strong skill. The fact that a person has no way to stop the sleight of hand person from taking the item I feel is the strong part. If the basic check succeeds (dc 20? please, of course this is a standard action) then the check is mainly just to do it unnoticed.
as for spellcraft though, what would a +15 item do for it nonepic? As that is a big bonus I'll just use the word 'always', even if it isnt necissarily true depending.
Always identify a spell being cast: Easy check to begin with, I dont mind the players knowing what is being cast most of the time. Those times I do care being out of line of sight tends to fix that problem
Always learn a spell from a spellbook or scroll: Cool, the player doesnt have to wait an extra level each time
Always prepare a spell from a borrowed spellbook: This I feel is one of the important ones, but it tends to be pretty easy even 'without' the bonus item. All it does is make it automatic a few levels earlier
Always know the school of magic when useing detect magic: I make my players roll this, but I always want them to succeed. Maybe I should get rid of the roll.hmm
Always identify a spell already in place: Cool
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Always identify materials made by a spell: Nice!
Always decipher a written spell without having to use read magic: this one is weird, I didnt even realize it was on there, interesting
Always determine what a spell that targetted you was after rolling the save: didnt know this one was here either, learn something new everyday! This one is pretty cool for the player, I am not sure if it would cause any problems, and it isnt an easy check.
Always identify a potion: cool
Always succeed at drawing a diagram to allow dimensional anchor to be cast on a magic circle spell: nice
Always understand a strange or unique magical effect, such as the effects of a magic stream: This one I think is the biggest, and it is something that I look forward to the players rolling successfully. After all, if they fail then they have to go to other spells (like divination) or head off to do research just to find out the initial stuff and then do these again to find out more. Skipping one bookkeeping step is big to me
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But then, this is the one that is least likely to be 'always' even with the item
So long as you dont go into the epic book I dont see any of these as being a problem. I could see an increase in cost based on some of it being pretty nice to the player, but really, what would be overpowered with spending a large chunk of cash and a bunch of skill points to always succeed at the above?