Both boots that you're looking at are good alternatives. The Moraine ($235) has morphed in recent years from a serious hiking boot to a good mid-weight mountaineering boot. Which is to say, it might be perfect for the kind of challenging adventures that you and your wife like to pursue. And, as it's built on a women's last, it ought to fit her well.
The Asolo 520 GTX ($200) is indeed a little lighter, both in terms of construction and actual weight. Consider also that you're paying perhaps $25 extra for a Gore-Tex bootie, something the Moraine doesn't have and frankly doesn't need. Still, the 520 is most definitely a sturdy off-trail boot, one that's highly regarded by gear testers.
I'd try on both, and just see what seems to make the most sense fit- and performance-wise. Also take a look at the Boreal Bulnes ($215), which straddle the 520 and Moraine in terms of weight and utility. A very nice boot.
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