Very slow OS responsiveness, excessive console error messages (1 per second)

I have a Mac Mini OSX Mountain Lion (now Mavericks) with 8GB of ram. I am a software developer and don't run extremely intensive applications concurrently on the system or anything that should be TOO memory intensive...

A few weeks ago I had an issue with the App Store doing an update of XCode. It took so long to simply click a button or even open the apple menu to restart. I once waited over 45 min for the Apple menu in the top left to open in order to shut down the computer properly...

Anyways, I finally narrowed down the problem to only occurring when the App Store was open, and it was trying to install the update for XCode. I waited days to see if it would finally finish, but the bar never moved... I finally just deleted XCode off of my computer completely and re-installed. This seemed to speed up everything again, and I was back to normal.

Yesterday I encountered some similar issues with the App Store, but a simple restart helped correct the issue.

Over the past few days I have noticed a major decline in performance and responsiveness.. Again I am not doing anything that should cause these slowdowns. It also takes a seemingly long time for the computer to go from off, to logged in and functional. I checked the Activity Monitor and everything seemed to be within normal limits, no odd readings, and the vast majority of my memory was not in use.

Today I decided that I would take a deeper look into the system to try and see if I could find any reasons for the issues. I opened the Console and I have potentially found a clue. I am getting the error mDNSResponder[42]: ERROR: send_all(34) wrote -1 of 4 errno 32 (Broken pipe) at the rate of exactly 1 per second, every second. It never stops.

Could this be a problem? Has anyone ever seen this before? Any known resolutions?

If I can't figure out how to speed this up, I am considering a complete re-install of the OS to get a fresh start.. How would I go about doing that? I don't have an install disk...

Problem was a bad hard drive, which should've been obvious, because it was slow getting things INTO memory, but CPU and RAM were nowhere near maxed out. Thank for the help everyone.