I understand your concerns... On most of my a/w 2005 and s/s 06 bbags the tassels are what I call "fluffy" which I guess is the same as what you call spongy. It annoys me a bit because you can see the fluffiness in between, but if it is any consolation, these types of tassels seem to withstand the splitting.
What would really bother me though, is if the bag had signs of use. Are you afraid yours was used because it was still available a year later? S/s 06 was a bad season for Bal, there are still bags from that season all around. I'm in Paris and last time I went to Bal there were about 10 emerald cities...
So, my point is: do you actually SEE signs of use on your bag? If yes, then return it right away! If not, don't worry!!
Let us know what you decide!!!