Well... I've had a couple of dry spells since my last post, but tonight I found both my ninth and tenth Structure up here.
I've been thinking about calling this area as-done-as-it-will-be in about a week: starting somewhere around 35-40 LY I found it increasingly difficult to see all the jumpable systems from my search center, so my coverage of the area has gotten patchy now in the 40-50 LY range.
I tend to jump out to a single visible system, then find six or eight more that weren't visible. So I jump to all of them and then back. A couple of times I've wandered out over 70 LY before I realized what I was doing.
Anyway, ten Structures are probably enough to tell me I'm a.) on the right track, and b.) still well below the upper boundary of the region. So it'll be back to the bubble soon to put my data together and then decide what's next.