The biggest change in the Linux boot CD in a long while has been upgrading the free version of Macrium to the same boot CD as the paid version. The main hassle with burning another boot CD is you should really test it before assuming it will work when the need arises. Sometimes I just can't get psyched to do yet another burn and boot test cycle esp. if there's nothing particularly new on the boot CD.
Short answer is, if you don't want to bother testing the new one, don't throw out the old one.
edit: otoh if you really like commenting your backup images then it may be worth the hassle since the new boot CD is supposed to support viewing the comments in the restore program.