speeding up a computer

I try not to re-boot computers, so over time, my main one slows down. I have noticed that after a week or so I am using about a gig of swap space. Usage seems to occur because on a nightly basis I run several rsync jobs to copy things to my NAS. One thing I have tried which helps somewhat is echo 3 > /proc/sys/vm/drop_caches and then to turn swap off and then on. This helps somewhat but speed is significantly below when the machine is initially booted. Can someone suggest an alternative strategy other than a regular re-boot?