Something I noticed - I'm sure you already know this Atwix, but it doesn't seem to be mentioned in your guide.
Occasionally, an heir can die while in regency. This leads to an Interregnum (you'll see this on the government screen for the target country), which will generally lead to a noble from another dynasty being placed on the throne (tough I've seen an interregnum where Austria ended up with a Habsburg...though I recall Austria does get Habsburg heirs via event if they aren't the ruling dynasty). Anyways, this is prime dynasty spreading opportunity, and what's even better is that
you don't even have to anticipate the heir death - you can RM them during the interregnum and get your dynasty installed.
Of course, you have to know that there's an interregnum. I believe that the only way an heir can die in regency is
via event - thus if you have your popups set correctly you should know exactly when this happens.
result in my case (those Skanderbeg genes!). England was married to Cornwall only at the time of heir death - RM during interregnum allowed dynasty spread:
They got immediate heir unfortunately, so cannot force PU immediately, but I am ready with boats.