I'll be there for Christmas and New Year also. It's very easy to find out what is going on out there at that time of the year because all the local are ever so friendly and accepting, as opposed to the high season.
I suggest to have a good read of the the "Ibiza in the Winter" section. Also whilst out there, go to Santa Gerturdis in the afternoon or early evening, and chat with the locals. Another great place is Guarana in Santa Eulalia, Mao's Room in Ibiza Town, etc.
It's all on this site, there's plenty to do and never a dull moment.
However, don't forget to visit the island during the day, I think you would miss something huge by only enjoying the nights out there.....
Just right click on the dancing people and see properties. Then you'll see the source address. I pissed myself loud the first time I saw them dancing, all four at the same time, hehehe, and even now I have a laugh when I watch them
As for your choices to NYE on the island. I think all the main night clubs will be open. Space will remain closed for alterations, and DC10 will set up the after-party instead. But I'm not sure of it all. The only sure thing is that Space will not open.
now that the exclusive about the space reform i gave you has been
confirmed, ill give you 2 more:
1- the circoloco terrace is now covered, not sure if this is going to
be just for new years day or forever, but the workers are working fast
to have everything ready.
2- there are works in the amnesia roof of the terrace too!