The 26th will be incredibly busy, the parade is usually every day from the 5th until after just New Years around 5PM or so. They usually do it around then so that Santa can light the big tree toward the end of the parade. (Which means right around the big Christmas tree in the New York area is probably the best place to watch it)
Since Blue Man is reserved seating it's not too bad, but I'm sure that show that day will be full.
They only had one concert last year and that was on a temporary stage, this year they have the new music plaza which is pretty nice. Mannheim Steamroller will be there that Saturday, so I'm sure a ton of locals will be out for that. There aren't any concerts the week after Christmas, but they usually have a ton of extra seasonal things going on (more actors out in the park, more of pretty much everything, and Universal 360 instead.. which is only running the week after Christmas)
