First, the Buquebus - very little difference in the classes - I'm not sure actually what the "special" is, I've only seen first and tourist. Like much transport out there, first gets slightly larger (and slightly is definitely operative here) seats. On the longer trips to Montevideo rather than Colonia it might make more of a difference, but not much. Also, I think you get a sandwich and a drink - but those are available from the cafeteria in tourist class, which is easily accessible. There's no distinction in boarding or leaving the boat, so it doesn't give you an advantage there, everyone lines up to get on or off together. My sense is it's not really worth it, on the other hand, it's not that much more expensive, so it's a personal choice. As I said, I'm not sure what "special" class is, I don't recall ever seeing it as an option, it must be something new.

I would book soon - on a holiday, with limited schedule, and lots of tourists in town, it's likely to book up.

New Year's Eve here BA closes up (Xmas Eve and Day too). They're considered family/friends time, and most businesses, including restaurants, tend to close and give their employees the day off. Hotel restaurants will be your best options, along with restaurants that cater more to a tourist crowd. There will, of course, be exceptions, and I noticed that last year there were more open than the year before, so who knows? But, if you have a place you want to eat at for NYE, I'd check early and book early. Most clubs will open pretty much at regular time, maybe slightly later, like 12:30 rather than 11:30/12:00.