In a rebuy I will set a predetermined amount I'm going to spend on rebuy's plus the add on. It will usually be 5X the buy-in.
My goal in a rebuy is to win the tournament, not just cash. I like to have at least 16,000 chips by the end of the rebuy period and will play a little looser. If there are three or more involved in an all in I'm not afraid to call with any two connectors or suited pockets in hopes of winning that pot. If I reach 5K or more I slow down and become more selective, but keep in mind that my 1st hour goal is 16K in chips. With ten minutes or less left in the rebuy period and I'm way short of that goal I will avoid any more rebuys or even the add on.
I seem to do ok in rebuy's following that pattern. It may or may not suit others.
The good thing about being short of my goal of 16 K is that many of those doing a lot of rebuys is that they have trouble changing gears and tightening up after the rebuy period. Keep an eye on them. You can pick up chips from them.