I can see the value of the add on during the break. The question is using the one re-buy in a deep stack tourney. There is usually an overlay in this tourney. Now other than getting it all in very good and getting the shaft....how aggressive do you play knowing you have the rebuy or do you just use it for the emergency bad beat bust out?
With rare exceptions, I think an add on is a waste of money. The value of an additional 2000 or whatever after an hour of play is much smaller than at the start of the tournament. Additionally, there is a decreasing marginal value of additional chips (first 1000 is worth more than the 2nd 1000, 2nd worth more than 3rd, etc.).
As far as rebuys go, I only rebuy if I'm knocked out early (for any reason). I don't adjust my play knowing I have a rebuy available.