If you seriously think this team needs to be blown up, then Allen to the Pacers without taking any salary back is the correct trade to make. You can hold out for a 1st rounder, but you need to settle for a 2nd round pick.
The reason is math. According to
ShamSports, the Celtics payroll is $79,205,308. Ray Allen makes $10,000,0000. The luxury tax threshold is $70,307,000. A salary dump, like what the Lakers did with Odom, is the sensible course if you want to throw in the towel on the season.
The Celtics a) save $10m in luxury tax, plus Allen's salary for the rest of the season and b) are further removed from having to pay the punitive luxury tax for repeat tax-payers in the future when a rebuilding process has hopefully become fruitful.