Huh. For some reason, I'm still getting crazy amounts of over-render as if there were no areaportals. Here's one example, featuring the area from before:
This could be helped by adding fade distances to the props inside BLU's spawn — far enough that you'd have to be on the other side of this stuff before they disappear, so you wouldn't even notice. Valve does this all the time. Even so, I'm confused why the areaportals (and I took the liberty of decompiling the map so I could confirm that they're where they should be) don't seem to be helping.
This one could maybe be fixed, or at least mitigated, by adding areaportals to the setup-gate doorways, but again I think adding fade distances to the far away props would be wise.