Tried searching, I know the search is broken, but I couldn't find these mentioned. They seem pretty obvious though, so forgive me if this isn't new.
For the Advent starbases:
1. The meteor attack does no damage. At least, against pirate corsairs they don't seem to do any damage.
2. The base doesn't shoot plasma bursts unless at least 1 plasma upgrade is researched. This may be a graphical thing, I can't tell if the damage is being done or not, but you don't see the balls of plasma shooting out unless you've reserached at least the first tech upgrade for them.