Looking at the converse issues, there are strong reasons for avoiding tantalum caps. In many environments you are banned from using them. They have two key problems - they present a fire hazard when they fail, and whiskers forming inside the capacitor can short the plates together. Most tantalums are used in situations where the current capacity of the system is adequate to blow out the tiny shorting whiskers, so you just see a hiccup in the system. Until this was figured out early electronic telecoms systems would give unexplained resets every now and then. Now they use solid aluminium electrolytics and ceramic capacitors, and you can see extremely long uptimes these days.
Hmm, never heard that as an operational mechanism. They do usually contain some silver, but it wouldn't make sense that it would be able to grow whiskers in that direction (i.e., through the solid electrolyte and into the dielectric).
My understanding is, the dielectric is normally cracked all over the place, it's just to a matter of degree; and where it's cracked, it can break down, which causes the electrolyte (MnO2) to heat up, release oxygen, and turn into Mn2O3, an insulator. Effectively self-healing the short. At manufacture, parts are tested to ratings, but the rating is easily halved from the stress of soldering; it's further reduced by strenuous environments (e.g., high supply ripple, wide temperature swings). The self-healing process is further aggravated by high peak current availability, such as unfused, low impedance supplies. (Which would seem to suggest that the voltage has to drop suddenly during the self-healing process, which could explain those random upset failures you mentioned. I haven't heard anything about it, probably because that would be a rather embarrassing failure mode -- talk about popcorn noise!)
The two theories (or arguably, hypotheses, depending on corroborating evidence) should exhibit much the same symptoms and effects, though. Or even, if it's just a matter of "whisker" being the presence of material, versus "crack" being a presumed absence, it's pretty much the same thing on a small enough scale (or if the crack happens to be filled with a 'whisker' of the solid electrolyte).
Tim