Picks 21-30 in the past decade or so have turned up three marginal all stars, and very few top rotation players. I wouldn't trade the 12th pick for the 22 and 24th, for example, even in a deep draft. If some team is hungry with quantity over quality, more power to them, and Ainge would probably be ready to oblige them/
2009 - Darren Collison, Rodrigue Beaubois, Taj Gibson
2008 - Ryan Anderson, Nicolas Batum, Serge Ibaka, George Hill
2007 - Wilson Chandler, Aaron Afflalo, Aaron Brooks, Tiago Splitter
2006 - Rajon Rondo, Kyle Lowry
2005 - David Lee
2004 - Delonte West, Tony Allen, Kevin Martin, Beno Udrih
2003 - Boris Diaw, Travis Outlaw, Kendrick Perkins, Leandor Barbosa, Josh Howard
2002 - Tayshaun Prince, Nenad Krstic, John Salmons
Those are just the best of the best, plenty of very solid rotation players or young guys that could still be stars (obviously Rondo stands out among that list, but there are plenty of other good starters in that mix).
The 12th Picks during that period - Melvin Ely, Nick Collison, Robert Swift, Yaroslav Korolev, Hilton Armstrong, Thaddeus Young, Jason Thompson, Gerald Henderson. Not exactly the cream of the crop coming out of the 12th pick from 2002-2009. In fact 2007 with Thad Young (and it is arguable) is the only year where you would even want the 12th pick over any of the players from 21-30 that I identified (there are plenty of crappy players in those picks as well, which aren't identified) nonetheless two players from 21-30. The 12th picks have been terrible of late.