Hey Tawna -
My old college roommates and I had a reunion weekend in Vegas over New Year's a few years back and it was so much fun we're thinking of doing it again.
Vegas is pretty great for New Years. Every year they close down the strip to motor traffic (except for the lane down the middle for emergency vehicles) for the big fireworks show, allowing lots of extra walking and standing room. We milled around the casinos watching special acts (some kind of cheesy, but totally fun) and wandering up and down the strip. All along the strip there are booths set up selling a beer and a shot for $5 so we just drank our way down the strip talking with people and having a great time. Then everyone watched the fireworks and went in search of a party.
We didn't end up buying tickets to any clubs, but we had a large group and kind of made our own party back in our own casino. If you really want to ensure you get into an event or club I would absolutely buy a ticket early. If you are just trying to make sure that you'll meet some people and have a great time, just go ANYWHERE on the strip and you'll find tons of people to party with. The strip basically turns into one giant party. Just watch where you decide to stop and hang out. I was on one side of the strip and it was fun, plenty of room to move, and mildly tame, while a friend of mine was on the other side and he had to lift girls over the barriers to keep them from getting squashed.
Personally, I wouldn't buy a ticket to a club or event because I like to leave my options open, but sometimes it's a good idea to give yourself a place to go. Especially since the clubs stay open so long and the parties might start to die around 1 or 2.
NOTE: If you are drinking your way down the strip, make sure to use the bathroom BEFORE the fireworks, because if you wait until after - well, GOOD LUCK!!
As for must see attractions: there are plenty of free attractions that are pretty cool: the lions at MGM Grand, the gorgeous Dale Chihuly glass sculpture on the ceiling of the Bellagio (my personal fav), as well as the fountain show in front of the Bellagio, the canals inside the Venetian are cool, the cobblestone streets and facade of the shopping area in NY, NY, and the Sirens of TI at Treasure Island seems like it would be cool (I've only seen the G rated pirate show they used to do - now it's the more R rated adult version of sirens and pirates).
Also, if you take a side trip to the old downtown section, check out the Fremont Street experience. It's pretty cool over on that side of town to see the really old Vegas and an older, more local type crowd. Also way cheaper over there! But note: a friend of mine works for Vegas Metro and always tells me not to go more than a block off of the main street (Freemont) because it turns into a bad neighborhood quickly and there are lots of muggings, etc. But it's easy to grab a cab from a casino right off of Freemont.
Stuff to spend your money on: If you like amusement rides, don't miss the rides on top of the Stratosphere. If you're into animals, there are tours in several casinos to see anything from dolphins to tigers - take your pick.
Let me know if you have questions about any specific thing you want to see or do. I used to go to Vegas all the time and have several friends who live there so I can give you more specific info if you want it.