Hi, Jim,
AZ might be ideal for the SPOT. Tree and cloud cover are known to degrade signal. Heavy forest canopy, even in N. AZ isn't all that common (open Ponderosa or a Apache Pine forest isn't exactly a heavy canopy), and clouds aren't that common. Even monsoons tend to have breaks, so the likelihood of getting a signal out is good. The only problem with a SPOT might be if you were in a canyon and couldn't get GPS lock because you couldn't get enough GPS satellites. Of course I'm speculating a bit here.
I'd be curious, if you've got a feel for it, as to how often your SPOT misses points. In other words, when you push "OK", does your "better half" consistently get a message with GPS coordinates? The biggest complaint I've read about the SPOT is that it misses a lot of points. I'd be particularly curious if you've tried it in "slot" type canyons where you have little view of the sky.
As for me, I went with the PLB. A PLB can be had for about $300 and there's no service fee. A SPOT II is about $150, and service is $100/year. At the end of two years, one would pay $350 for a SPOT but only $300 for a PLB. Of course you can't test a PLB the same way you can a SPOT by constantly clicking OK and seeing if a message gets through. Still, I like the fact that the signal is stronger on a PLB and that it sends out a homing beacon and that one's position can be determined with a PLB even if the device can't get a GPS lock. Wish I could put the two in a blender and get the best of both.

HJ