Parties that include dinner also? That is a new one!
Usually Spaniards spend New Year's Eve with their families. They eat dinner together, eat the grapes, bring in the New Year, and then the younger people in the family head off to parties with their friends. So on new years eve, things don't start to pick up until 1:30 or so because everyone it getting to their parties, meeting up with their friends etc.
The past few years, these parties have gotten more and more expensive, outrageously so. Even though they promise you unlimited drinks, how many are you really going to be able to get in a crowded bar?! So, the trick is to, if you know some locals, to find out if they know a good place... my friends and I have found this awesome little place that's cool, plays good music, room to dance, gets full- but not too much, and there is NO problem in getting our drinks!
But after going to the same place for a few years... well, the new trend is leading to renting an apt. or bar or some other local between your group of friends- you have control over the bar etc, and know it won't get overcrowded... or gathering at somebodys home and celebrating there. So the expensive parties are still out there... but looks like its probably one of the few alternatives a tourist has if they don't know anybody from there.
There is always bar hopping, but its hard to do unless you research it ahead of time- find out what bars will not be booked for private parties, or having parties at all, but just be open to walk-ins. This last, the walk-in, are few and far in-between on New Years.