I think you need to be asking yourself some other questions here. First of all, how much money are you willing to spend on the tournament? If it's $10 per rebuy are you willing to rebuy 4 or 5 times just because it's available to make it a $50 tournament? If not, then you should treat each hand as though it were a single-buy-in and save the rebuys for near the end of the rebuy period (for instance, if you have 1K and a rebuy gets you 5K then just before the rebuy period is over go into double-up or bust mode so you don't leave the rebuy period with only 1K).
Second, how far do you think you'll make it in the tournament? Are you expecting to Min-cash it? If so, then avoid rebuys at all costs. Look at it this way, if a min-cash gets you 200% of your buy-in, you have to min-cash just to break even after a single rebuy. If you rebuy 3 or 4 times then you've got to make a moderate run into the money just to break even. Only be a rebuyer if you are confident that you can place well into the money to make up for it.
Third, consider the value of the rebuy chips. Let's say a buy-in gets you 5K in chips. At level 1 that could be worth 250 BBs when blinds are 10/20. An hour or two into the tourney that value can drop to 25BBs when the blinds are at 100/200. That means the hands-to-stack ratio decreases dramatically (i.e. the amount of time you can realistically last on the rebuy lowers drastically the long the rebuy period lasts).
Finally, would the rebuy help or hurt you? If you've got a stack of 35K and the rebuy is only 5K you may want to reconsider going all-in. Treat the hand the same way you would treat losing the tournament completely because giving up that many chips is crippling enough that you may want to consider just not rebuying.
For me, rebuying is always a "necessary evil". If I'm in a $2 tourney and the prize pool is $1k GTD then I'll rebuy, but I'll do it grudgingly.