That's great that your library has the first three sets; I wish mine did!
I did get the box set for Christmas, and so decided to donate my own season sets to my old Preschool. I wasn't entirely sure they would take them, so I wrote an impassioned email about why Fraggle Rock is still relevant to children today, hehe. Thankfully they accepted and appreciated the offer.
There are a lot of people who haven't been able to buy the first three sets yet, nevermind the box set, so I definitely recommend donating them to a school or library.