i think it depends on your stack size compared to the average as well. If you are well chipped but on average (ie a wild rebuy) you should take it, as those 3k chips (say) could represent a whole lot more if you double through x amount of times, or could save your tourney if you get crippled.
i just always add on because that"s the way i am. A few weeks ago i had 90k in the 3r at the break and still added on...