We're lucky in Sunset Park where marathon watching is concerned. The leaders come by early enough that you can go pick up a bagel at Sunset Bagels, a cafe con leche at Gran Via, and then walk down to 4th Avenue to check out how they're doing. After an hour or so of cheering on the faster folks, you can stop over to Eclipse or International or Georges for some Sunday vittles only to return to cheer on the slower folks (who still have the energy to smile and/or wave back). Also, the people in costume still have the costumes when they get to us.
Check out some great info about the entire route here.