Yeah, I think getting dementia rather forces one to more and more treasure the little things ... as the big things simply become too vast for one's mind to envelop. The little pleasures of visiting a child, or sharing a name with someone. These are largely the only pleasures a dementia victim has left.
So sorry to hear about your ex's grandmother, and what your MIL went through trying to keep up with caregiving. LV's mother also had dementia, probably the same type -- at about the same age -- so I think it was genetic. Wasn't much of a comfort to think so, though.
Love means never having to say, "Put down that meat cleaver!"