Well, we probably shouldn't be doing anything in either country to begin with... how about first finishing what we started elsewhere?
If "kinetic military action" were taken in Syria, wouldn't Iran light the fuse in Iraq sending us back to 2007? Increased Iranian interference in Afghanistan might be a consequence too. Iran has a couple of warships in the Med... could an "incident" with them occur off the Syrian coast sparking a large scale confrontation?
What about Hezbollah? I don't know just how responsive they really are to Syria, but my guess is that they would try to start something with Israel in retaliation to US raids which just might prompt another Lebanon invasion. And Israel probably would not be well served by getting in to a war (for whatever reason) with any Arab country in the midst of all the revolts and anger going on. With Mubarak gone and pissed off Egyptians potentially swaying their military, who is going to guarantee Egypt remains nice and passive in what might be viewed as another Jew v. Arab war?
To top it off there likely would be very little international support for a UN resolution against Syria's government, even if there were, Russia or China would have probably vetoed it and the US would have to go-it-alone yet again further compromising it's image and credibility in the region. And stretching resources some more.
Gaddafi on the other hand was a conveniently crazy, isolated, easy target that
was supposed to go away really fast, and most important of all: the UK, France and other Euro ally countries rely quite a bit on Libyan oil exports. They have a vested interest in Libya and apparently so do we by matter of association with them.