You should absolutely not be playing tight early on in rebuy tournaments unless you want to let everyone else have advantage over you when the rebuy period ends. You should go into a rebuy tournament knowing that you are willing to spend another 5-15?BI's on rebuys. You want to get your money in with much more marginal hands than usual because you're just looking to build build build.
Also, if you are playing a rebuy and don't do an initial double buyin or if you don't take the addon at the end of the rebuy period, you are automatically labeled as a huge donk because you obviously don't know how to play rebuys.
If you're looking for something a little more solid, here is the CardsChat article on how to play rebuys: http://www.cardschat.com/rebuy-tournament-strategy.php
Not sure if it's outdated at all, I haven't read it in a LONG time, but I'm sure most of it will still be applicable.