I want to reset my iMac to factory settings but want to save my iTunes library first. Is that possible?

I have an older iMac (first of the Intel Duo Core) that is running extremely slowly - the rainbow ball spins for 30 seconds between most clicks. I think it's just overloaded with too much old stuff. I have most of my files stored on Dropbox. I want to restore it to the factory settings before giving up and buying a new computer. I don't want to restore from my time machine because I don't want to bring along the old problems. I have saved my iPhoto libray to an external drive. Can I do the same with my iTunes? Or can I somehow sync it to my iPad, iPhone or Air so that I don't lose my music? If so, can you tell me how? Also, this computer is too old to sync to iCloud. Thank you for any help you can give!