I finished this job today. Prepping the boards was really tedious, but not difficult. Getting the new material on and looking nice wasn't difficult either, I just had to be careful with my usually club like hands. However, with the center headliners, I wrapped the material back around on the boards, having forgotten that the material originally wraps up and glues on to the body. So it looks a little weird with some exposed fiberglass right beneath the weatherstripping.
But the headliners are now new, clean, and not sagging into my face.
Honestly, the biggest bitch during this job was getting the sun visors back in. The screws that hold them on are very short, and my new headliner has a noticeably thicker backing foam. This meant that the original sun visor screws could not reach their receptacles anymore. So I just grabbed some longer M5 bolts out of my pile of random crap, and things went back in just fine at that point.
Not a perfectly done job on my part, but I think it still looks pretty darned good, and good enough to not have spent the insane $600 on the fiberglass units.