although I sometimes think people give mercury super-powers and call out the hazmat team when they break a CFL 
Breaking a single CFL indeed does nothing, it is the waste from 1000's lamps what becomes the problem.
But the problem with mercury and airplanes has nothing to do with its toxicity. In the contrary, it has a lot of to do with the very low mercury reactivity even when liquid, beside dissolving metals. In fact any inert liquid metal will present the same problem:
Many metals very like to dissolve each other, when they have the chance to move around in their pure form, mainly when they alone do not exhibit that high melting point and one of them is already liquid.
So when the Hg comes into contact with a clean aluminum, it starts to dissolve it. Because the Hg is rather non reactive with oxygen, it remains clean on its surface. So when some other metal, like the aluminum is dissolved in it, such metal becomes exposed as well. And because the aluminum is very reactive with the oxygen, it immediately starts to oxidize there. That oxidation makes a crust, which because not supported, immediately turns into dust. Because that means aluminum gets lost from the Hg, it allows more aluminum to get dissolved and the cycle repeats over and over, till the Hg does not get somehow inhibited. And because Hg is rather inert and even does not evaporate that fast, it does not happen that soon even with a small drop of mercury And because that dust is insoluble in virtually anything, it remains on the surface. And because it is a dust, it lets the air, with the oxygen, pass through, to continue supporting the oxidation.
Now because being so reactive, Al normally is not clean, but always has a very hard coat of oxide layer which stops the further oxidation. But that layer is rather brittle and because the aluminum is rather soft, it tends to break. Again, normally with aluminum in normal environment, like air or water, new oxide reforms practically instantly, so macroscopically nothing happens. But once that scratch forms under a drop of mercury, the "show" starts and mercury starts to act like the catalyst allowing the aluminum to continually oxidize through without the oxide layer ever stopping it.
And why it is so big problem with aircrafts? Because in most of them aluminum is used for most of the structural components (although in modern jets it is on many places getting replaced by various laminates). So even a small Hg spill may easily start quite severe destruction, practically ruining a nearly-billion$ worth aircraft within a year or so, so within few percents of its designed life. And on top of that because the mercury is electrically conductive, the common aluminum structure inspection methods using eddy currents won't show that damage in time.
For this risk, the Hg has to be in the liquid form. So most fluorescents are safe: The Hg is there already in a solid amalgam, so it is not liquid (a necessary condition for that damage type). Plus really small quantities (talking about quantities like the mg dose in fluorescents) will evaporate and vent out before it reaches any structural part. But gram quantities start to be a problem when they reach some critical component (where is not that much material to eat before it becomes too weak to be safe), definitely amount of a comparable volume like there is of the Na in the SOX would be quite a risk.
Same as mercury, other metals (or alloys, liquid at room temperature), like Gallium, are for that same reason very risky as well, but not that potent as the Hg (because of so low melting point of Hg), plus mainly unlike the mercury, those metals were never used so widely in things for general public as the Hg was.
Sodium is safe from this perspective (not from the eventual fire hazard of course), as first it is solid at room temperature, so can not work in that cycle, plus it is very reactive, so will oxidize by itself, so nothing will remain to cause any damage to the aircraft aluminum parts.
