the "flaw" and security risk seem rather minimal if you DON'T use the internet at Starbucks or other free places, does the upgrade fix more than just the security issue?
Pro's
You're up to date
New map app that sends directions to phones/pads
iBooks for reading purchased books on your mac
Optimized for notebook use
Multi-monitor support improved
Con's
Not compatible with as many 3rd party agents/daemons/ktext as ML
iTunes/iPhoto databases modified so dual booting older OS is a problem
Optimized for notebook use
iTunes/iPhone local sync gone
iTunes/books local management gone
External drive sleep issues with some manufacturers
HDMI display issues with some monitors
Has a larger OS footprint, runs more data collection (systemstats)
Have a good working clone so you can go back if you do upgrade, you may be one of the unlucky ones who's 3rd party stuff hose your system. Be prepared to do a clean install (have all your installers handy) if you are again one of the unlucky but still want Mavericks.
Full disclosure: I use Mavericks on my MacBook Air but continue to use Mountain Lion on my Mac Pro.