1.) As Muslims we have our own Hijri calendar, we must reject gregorian calendar because it is not from Islam. The gregorian calendar was made by Pope Gregory (a pagan worshipper). According to our hijri calendar the new year actually begins on the first of Muharram.
Calendars are just conventions to register dates. They do not serve a moral or ethical purpose.
It seems to me that it comes down to how willing Muslims will be to celebrate with non-Muslims.
2.) On such a day majority of people listen to music, drink alcohol and commit adultery.
This is a great evil and a Muslim should stay away from such things.
I don`t see the problem with listening to music, and I don`t think adultery or even alcohol usage rise very much due to the commemorations of New Year`s Eve.
3.) It is against the spirit of Islam.
How so?
4.) What exactly is there to celebrate?
For many people it is a convenient time to remind ourselves to keep some perspective, show gratitude for our joys and gifts, and a measure of reconsideration for our goals for the future.
Thousands of Muslims are dying and starving to death in Africa, Afghanistan, Syria, Iraq...etc and you want to enjoy your life?
Are people not expected to want to enjoy their lives, regardless of how much grief, sorrow or compassion they may see fit to have for others?
Let them eat and enjoy themselves and be diverted by [false] hope, for they are going to know. 15:3
What would make hopes for a happy new year "false"?