A New Spell, "Know Thy Enemy"

I am one of those DM's that doesn't let Players know the AC or "To Hit" information about their opponents.  One of the reasons for this is because I don't see how a PC would know such information about an opponent.  I have other reasons, but in considering this and Players who press me to let them know what they need to roll "to hit".

I believe I have come up with a livable alternative for me.  A new spell, usable Clerics and MU's called "Know Thy Enemy".  When a Cleric or MU casts the spell  (presumably the first thing they do) they are able to know who or what it is and the AC of the opponent is made known to the spellcaster who can then inform the rest of the party if they so choose to do so.  Knowledge is power after all.

At that point, a Player can then make use of THAC0 information to know for themselves what they need "to hit" and maybe even get a +1 bonus for the knowledge (I haven't made up my mind on that last bit yet).

To gain that information costs a spell caster a spell slot for the day though and I am likely to make it a 3rd or 4th level spell. scratch that, I think this is just a firsts level spell after all.  I will also enforce  a material component check for the spell to be cast as well requiring something rare and which is destroyed or used up at the casting of the spell each time, requiring the spell caster to keep plenty of that hard to find and obtain component on hand. 

The item in question will be an "eye" tooth/fang from a defeated opponent.  The tooth will crumble into dust upon casting the spell.  The tooth will have to be obtained by the spell caster themself in order for it to work.