so the text for banishment says that a light wizard within 12" of the caster increases the strength of the spell. there is no stipulation that the wizard even be from the caster's own side. what's your guys' take on this? do enemy wizards bump the strength of my banishments and vice versa?

From a fluff perspective it would sound logical that even enemy wizards count to this as they somehow draw light energies around them and stuff. So I would say yes, you can use enemy wizards too.

As it doesn't specify friendly wizards I would assume that yes, you count all all wizards.

I would look at previous faq rulings like this:

Q. In a Daemon vs. Daemon battle, does the Standard of Chaos
Glory affect Daemons on both sides? (p95)
A. No.

I would assume the answer is: No, your opponent isn't helping you! Ever!

And errata before that said:
"Yes! Let the chaos reign!" or something like that standard of chaos question. I still have that errata printed at home. They change their mind all the time and some answers are very irrational (like flaming sword buff).

I remember both! but one of them was for 7th (let chaos regin ) the newer one is for 8th edition !
Also for Epidemus spec in the erreta you only count the wounds caused by your army regardless if your enemy also have nurgle deamons !

no, that bit about epi is not in the errata, and in fact the AB says to count the wounds from both sides.

To be fair though; there's not much point citing ver1.3 if ver1.4 (for example) says the opposite thing entirely. I don't think you can just mix and match rule 'clarifications' willy nilly as they suit you, because... surely that just sounds stupid?

Whoa, careful not to sound rude FeeZ... Besides, I think his point was just that the errata changes all the time. He's not trying to use that as justification to say "it said this before so that's the rule I'm following." His point is just that they change their mind all the time. (Sorry if I misinterpreted you Kitsune!)