Not intending to go off-topic here, though I figured it is related and is worth a mention.
I know that given the complexities of tabletop vs.what can actually can be put into code makes some aspects of D&D impossible to implement... it may be the limited number of spells in some spheres is the reason why barred spheres are currently set for you. I am not sure, though this is what the WoTC 3.5 Core PHB has as far as wizard specialists go:
A specialist wizard can prepare one additional spell of her specialty school per spell level. She also gains a +2 bonus on Spellcraft checks to learn the spells of her chosen school. The wizard must choose whether to specialize and, if she does so, choose her specialty at 1st level. At this time, she must also give up two other schools of magic (unless she chooses to specialize in divination), which become her prohibited schools. For instance, if she chooses to specialize in conjuration, she might decide to give up enchantment and necromancy, or evocation and transmutation. A wizard can never give up divination to fulfill this requirement. Spells of of the prohibited school or schools are not available to the wizard, and she can't even cast such spells from scrolls or fire them from wands. She may not change either her specialization or her prohibited schools later.
To me, this seems a much easier way to go about specializing. Have the wizard choose at creation, and also choose their barred schools. If they choose not to specialize, then they are considered a Mage. This way, you will not need to join a guild to have access to spells above 1st level, races who currently do not have guilds that accept them will not have to email to specialize, and even the first level spells of your prohibited schools would be unavailable to you.
Perhaps make joining a guild as a way to gain access to the more advanced spells of your specialization that you cannot learn anywhere else.
It would also take care of some un-IC issues that I have noticed... i.e. all wizards MUST graduate the School of Wonder(a School founded by a good-aligned deity), regardless of alignment to specialize or gain spells past the first level. It seems very unlikely to me that one of an evil nature would be permitted entrance, much less allowed to study there.