Organizing a group for magicians is a fine idea. In order to prevent secret-searchers from abusing the privelege, teach only very basic sleight of hand. Only reveal secrets that can be found in every basic magic book available at any book store. If the student is serious about learning magic, this will not frustrate him. If he is only there to learn the method behind Criss Angel's levitation, he won't put up with a few hours of learning the Overhand Shuffle. Furthermore, he probably will not return.
Hold meetings at which magicians may perform whatever material on which they hope to improve, such that they may get advice on doing so. However, don't focus on trading secrets. An organization of magicians that only meets to talk about the latest in sleights creates disorganized magicians who don't make any progress as performers. Focus on perfecting one piece by workshopping it at every consecutive meeting until it reaches a point at which the student is satisfied that it is well-polished. This is an approach that was taken in my acting classes during university, and it makes sense as applied to magic. Magic meetings should not be about performing one trick and getting compliments; they should be centered around perfecting specific routines through repetition and criticism. Routines and acts aren't complete when they've been practiced a thousand times and scripted. They simply get better and better as new adjustments are made.
Hence, I say that you should encourage students to come in order to learn in a stepwise fashion until they can perform one trick. Once that trick is mastered, they bring their performance to the meeting and take "director's notes" of a sort from those watching. Incorporating those notes, the student runs the routine again, repeating the process. Once the student has some new ideas to incorporate into the routine, he may incorporate those ideas and work the routine in front of lay audiences between meetings. With those experiences under his belt, he gets an idea of what points of the routine are strong, which "director's notes" were worth using, and which didn't improve the audience's experience.
This sort of approach that has two specific advantages:
1. By teaching basic sleight of hand first, along with simple effects that can be found fairly easily, you protect the "deeper" secrets of magic, and you encourage habits that will benefit novices.
2. Focusing on presentation and workshopping one routine at a time over many weeks allows students to build a strong repertoire slowly but surely. Furthermore, by performing for lay audiences between workshops, the student gains confidence, a sense of what it is like to perform, and gets the best advice possible from guaging the interaction.
I have attended magic club meetings in which magicians simply perform new tricks every week, then proceed in such a fashion ad infinitum in an attempt to fool each other and impress each other. They care very little about how their routines might be received by non-magician audiences. This is dangerous for the novice members of these clubs, since they pick up the habit of jumping from trick to trick without focusing any attention on presentation.
I can say that 4 years of membership in a club of this sort had absolutely no positive effect on my magic as it was received by the lay public. Had the meetings focused on mastering one effect, performing it for the club, getting advice, applying advice, taking notes, and repeating the process, I am sure that much larger bounds in improvement could have been made.
On a final note, you should not have too much fear over thieves of secrets. YouTube is the ultimate exposure tool, and probably the most detrimental to magic secrecy. However, even YouTube doesn't affect well-performed magic. The secret only constitutes a small percentage of the important aspects involved in presenting illusions.