If your add ons folder has a "-" in the name (ie "Add-ons") then it won't work. It has to be "AddOns" (no spaces, dashes, periods or commas).
The variable names don't need to be in quote marks. Only the values need to be.
Can you post a copy of your latest.log file? That might help track down the problem.
... Okay, so it seems some previous version of Oolite created the "Add-ons" directory, which is where I'd been stuffing all my addons. And now, after renaming it to "AddOns", getting a pile of warnings about duplicate OXPs, cleaning the whole thing out of extras, double-checking versions, and suchlike... there, in the F3 menu, is the 'Home System Privileges' option. (And a few other things that I'd installed but had never noticed had never shown up in-game.)
... And it looks like I was completely wrong about downloaded OXPs showing up in the Expansions menu.
So, uh... thanks.
(In case anyone's curious - I now have 5 OXZs and 177 OXPs left in that folder, though right now I couldn't say how many of them actually contain things I want to keep playing with...)