A. always have a current backup first.
B. erase your drive and do a restore with superduper.
C. Intech SpeedTools Suite has a file defgrag utility BUT watch out if it tries to defrag a 20GB+ file! ( have those on their own partition anyway, mostly backup images of other volumes that run 16-65GB).
D. Keep your drive to 65% or less, even more so for boot drive.
E. do some cleaning of temp and cache folders, which is something that SuperDuper does for you, it skips backing them up because those are best recreated fresh by the OS.
F. when you restore, SuperDuper organizes directories into a "smarter" order.
G. It does improve performance.
H. While at it, install a new 500GB drive why not.
I. Use the old drive for backups and emergency boot drive.