My strategy in a rebuy depends if there's an addon after the rebuy period. If there's an addon, to be honest I'll try to survive the rebuy period losing minimal chips until the addon break. After the addon break, that's when I start hunting for a double up.
Rebuys are good, because more players join during late registration, and rebuys boost the prizepool. I'll never rebuy more than 3 bullets in any game, usually 2 max depending on players/prizes.