Anyhow, here's how I'm getting on in my current game: Difficulty and AI Agressiveness both set to Normal.
As Castille I've had constant wars since 1066. The first, which finished off Cuenca and Zaragosa, lasted until around 1074, during which period I was able to both win against the Muslims
and build province improvements more or less continuously. Toledo also came out of the other end severely bruised - reduced to one province.
A short cessation of hostilities between 1074-78 allowed me to regroup before succesive (and succesful) wars against;
Valencia - stabbed in the back whilst they were fighting Sevilla
Palermo - target of first Crusade called in 1068, taken by Castille in 1078. DOWed immediately after assasinating the encumbent Emir - which thus ended their alliance with the far too powerful Zirid*
Mallorca - stabbed in the back whilst they were fighting Sevilla
Catalonia and
Aragon - who DOWed my ally, Navarre
has left me, in 1097, here (Palermo and Agrigento off map);
The only real fly in the ointment is the fact that I allied, at the outset, with England and Germany - which allowed them to take Zaragosa and Tarragona respectively during the first war. Both present real obstacles to my goal of uniting Spain......
The "fertility" stuff seems to be working fine; Sancho died without issue, despite my best efforts (three wives, two assasinations) - the guy is definitely firing blanks

. Garcia met the same fate, leaving Alfonso to inherit**. And as he seems unable to sire anything but wenches, the stage is set fair for Sancho of Navarre to clear the table - without really ever having to show his hand.
No CTDs yet.
* - perhaps another argument for adjusting the alliance system? It certainly felt like an exploit to me. Maybe allow alliances to persist even upon the death of a King/Duke/Count?
** - little bit of a scripting bug here? Alfonso aquired a "bastard" son, Rodrigo - 1068-69. I got the "bastard trait" option screen ("He's no son of mine" being one of the options) a couple of years after Sancho died and I had begun to play as Alfonso. But this was in 1085 - Rodrigo was sixteen years dead at this point.
(apologies for the half-arsed AAR style of this post - maybe now I've figured out the screenie thing I'll try a proper one

)