An update: Switching from css-as-files to css-as-database (via AdminCP > Settings > Options > Style & Language settings ) and allowing overwrite during installation (even though I had theoretically uninstalled all previous versions of VBO via the "uninstall" option) appears to have at least removed the asterisks and given me usable error messages.
Now the problem is as follows:
-- I go to vB Optimise > Main Settings
-- I hit the "Yes" radio button in the "Online / Offline" area. I hit "save" at page bottom.
-- The page reloads, showing my desired settings
-- The "system test" screen, however, says that "vB Optimise is currently offline. Please enable and configure vB Optimise to run a system test."
If I log out and back in, the main settings screen still shows VBO as being on, and the system test still complains about it being off.
For context, here's what the "Optimal Settings" test results look like:
http://i1337.photobucket.com/albums/...psd4125f3d.jpg
Are there any common steps to take from here?