I'm going to take a slightly different view than the majority of the PP's here.
If you don't feel up to it, don't go. This isn't about "do whatever makes you happy and sod anyone else," but I sure as shit wouldn't want someone attending something I was hosting who was sitting there, clock watching for an appropriate time to leave.
Of course, if this is a habit of yours, you may lose friends over it or those friends may become reluctant to make future plans with you. This is a consequence of prioritising yourself, and if it's one that you're happy to risk, then do it.
It does sound like from your nostalgia comment that this is a group of friends that you were once close to and are now less close to but maybe trying to stick together for the nostalgia? Am I reading that right? So, is it a case of you accepting that these friendships have maybe already ran their course and you're ready to move on? Is that one of the reasons you feel less enthused about spending the night with them? Do you think if you go to the NYE party there's a chance that these friendships could be reinvigorated and is that something you may want? If so, I think you should go and see what happens. If not, then, well, there's your answer.
And no one has a magic ball that we can see into the future and see what mood we will all be in on NYE and know if we should make plans or not based on how we feel. Sometimes, you make plans when you feel up to it and you talk yourself into it and then when it rolls around, you realise that you're just not up to it.
You could force yourself to go and you may enjoy it, OP. However, if you think you're just going to be clock watching for the best time to leave, I wouldn't bother. I wouldn't want to be a host of a party where people, even one guest, was sat, waiting to announce their exit.