Troubleshooting a slow Mac - OSX 10.9.5
The three simplest things to do to troubleshoot slowness is to write down what specifically you wish to optimize and then measure it. When you have a good baseline and preferably can reliably reproduce the conditions when it's slow.


Make a new empty user and set the Mac to not auto log in. Reboot and repeat the test with the new account.
Look in the console logs for storage errors and boot into recovery mode to run Disk Utility to check for catalog or other errors.
Install a clean OS onto a USB drive and boot from that. As long as the drive is reasonably fast, you should be a bit slower on the external drive and could even point a user home folder there back to the home folder on the internal drive to see if it's a system issue.


Unfortunately, I don't have a silver bullet, but once you narrow down things to user level slowness or system slowness or hardware errors/degradation then you can dig into Activity Monitor and see if CPU or RAM or storage is constrained when your slowness arrives. From your snapshots, you have plenty of RAM and the system should only get faster with use as files needed get cached in RAM. Your CPU doesn't look loaded at all, so I'm guessing network or storage issues from the data you have provided.