It all depends on what you're willing to lose, 
worst-case scenario. If you don't give yourself a 
safety net, you might happen, by a stroke of bad 
luck, to be that *one* that gets lost without a 
trace. People have posted to the board about 
losing insured airmail and losing EMS packages... 
but there's not much you can do if you don't take 
the few extra dollars to cover your purchase. If 
you're willing to not only lose the cels, but the 
money that you spent on them--- that's up to you. 
^_^

I once lost a package from Canada to the US, but 
it was insured. I always insure everything, 
whether it's a triple-digit cel package or a $5 
manga volume, just because I want that security.

Chances are, nothing will happen to your package 
at all. As people have pointed out, the US and 
Japanese postal systems are excellent and 
reliable. However, insurance is to protect you 
from accidents that no one can predict. ^_^

-Cres