In tournaments with an add-on, my first goal is to make it to the add-on period and then purchase the add-on, since these chips are cheaper than the rest of the chips. Purchasing the add-on is probably the easiest edge, you can find anywhere in poker, as long as there are people not doing it. So for me it makes no sense to play an R+A tournament, if you are not willing to purchase the add-on. And to reach that goal rebuys will sometimes be nessesary. For R+A events I recommend a bankroll of at least 250 BIs, whereas for other MTTs 100 BIs are enough. So 550$ for a 2,2$ R+A and 1.375$ for a 5,5$ R+A. Or at least something in that ballpark.
In tournaments without an add-on, there is no difference between reentering and simply playing another one, and reentering a tournament 4 times is no more detrimental to the bankroll than playing 5 similar tournaments and not cashing in the first 4. For me the decision to reenter or not should be based upon, how far the tournament has progressed, what other tournaments are now available, and if the tournament seem to be soft.
On
888 Poker you get to keep your seat, so if its a really good table, that is certainly a valid reason for reentering. There are also not that many tournaments running, so if I bust early, the choise might be between reentering or wait 30 minutes for the next one to begin. On
pokerstars I rarely reenter, because you dont get to keep your seat, and there are so many tournaments running, that usually I prefer to just buy into another one. But if I run kings into aces 13 minutes into the tournament and get felted, then why not reenter. There was probably a reason, why I wanted to play that tournament in the first place, and that reason has not changed in 13 minutes.