Q: Old MacKeeper--should I dump it?

Hi ..

Uninstall MacKeeper. You don't need it on your Mac anymore than anti virus software. Your Mac has System Integrity Protection built in > About System Integrity Protection on your Mac - Apple Support

Instructions for uninstalling MacKeeper here > http://www.macworld.com/article/2861435/software-utilities/how-to-uninstall-mack eeper-from-your-mac.html

For security, make sure your OS X is up to date.

Click your Apple  top left in your screen.

From the drop down menu click About this Mac

Make sure the Overview tab is selected then click Software Update.

Your Mac may restart several times during the update process. That’s ok.

You can have your Mac automatically check for updates in System Preferences > App Store.

So should I uninstall MacK?

Absolutely!

MacKeeper's a scam, and you should be concerned if you used it to remove any of the so-called "unneeded stuff" it found. Yes, you should uninstall it.

Anti-virus software and "maintenance" software is not needed.  OS X itself has all the virus protection it needs and the operating system can maintain itself.  Granted some software such as OmniDiskSweeper and EtreCheck can be useful but applications like MacKeeper, MacCleaner, etc... should be avoided. 

dump the old one, dump the new one, dump the one in between, primitively dump the next one as well.

The software has been cited on this forum and others as continually making claims and services it does not provide, as well as causing a host of issues.