I'm going to agree with buckeyebama that the crowds are likely to be somewhat higher for 2017's marathon weekend than, say, years when the marathon was later, such as Jan. 12. It's entirely possible that some school/holiday breaks will continue through the week before the races and crowds will stay larger until after marathon day (Jan. 8 this year).
Having run there many years now, that seems to be the trend. The week or two AFTER the marathon is usually good. The days before the marathon are more dependent on holiday/school schedules.