Hmmm, well my basic thoughts on the subject are mixed. To be honest the entire "wigger" thing has been going on for a VERY long time now, having started in the 1990s. Guys like John Cena have pretty much made a career out of it.
On one hand I don't see this as being any worse than say "Talk Like a Pirate" day or something like that. To be honest, the general behavior of the wiggers is cribbed DIRECTLY from the way blacks behave, as opposed to being based on some kind of broad stereotype, and that's what makes it a touchy subject. Basically, it's sort of like any other clique where someone does something perceived as cool, and then everyone wants to imitate them. In this case it's the behaviors associated with a racial subculture. Your pretty much seeing the white kids looking at how the black kids behave and public, get away with it, and then imitating the same thing.
In general I tend to think that this kind of black culture is kind of divisive to begin with, and something that should be being overcome, as it actually creates problems and what little remains of racial tensions to begin with. To be honest if Black America looks at the wiggers and thinks "okay, that's idiotic, acting like that and getting away with it makes us look like douchebags" and it helps destroy that aspect of Black culture, it's a win-win situation for everyone.
It should be understood that this is not a commentary on all Blacks, but a specific aspect of the culture. The whole "wigger" thing does not claim to be imitating everyone with that skin color, but a very specific group of people. It differs from blackface in this respect. In general the people doing the "wigger" thing do it because they want to be that way, as opposed to mocking it.
On the other hand, for all the reasons why it's not offensive and offhanded positive occurances it can have, the question remains whether or not this belongs in school. The school isn't apparently doing it to point out the problems or make a statement, but because this is something the kids themselves are embracing, and they are hoping that it will make the school seem more "hip" and appealing to the students. In doing so it's encouraging ridiculous behavior both in the terms of the so called "wiggers" and the people they are emulating.
That said, I think the worst stereotype in this whole thing is the person trying to sue the school for personal gain over this. THAT is even more ridiculous than the whole idea of Wigger Day to begin with.