I agree with both sides of the argument, depending on the circumstances.

I can think of many situations when taking Navarre and/or Aragon would be more trouble than they're worth, especially if the Aragonese king has spawned a few sons. In this case, defending against Aragon is much less costly, resource-wise, than taking it. When you've got hordes of Muslims clamouring in the South, this is an important factor.

Also, remember that a Metalsmith takes 6 years to develop. In the early part of a campaign especially, that can be a looong time. THEN you've got to build your unit requirements. Navarre comes with bugger-all in the way of buildings.

You've gotta be pretty stable and free of Almohad threat to consider either, IMHO.

Sure, you can go for the iron-rich provinces early on (to gain an early edge), but you risk much in the meantime. Basically, 6 opportunities for the Almos to have a crack at your more important homeland provinces with decreased garrisons.

But yeah, the additional Jinette-training facilities may justify it altogether - again, depending on the circumstances.