I have to agree with Starhound about the Advent mines. I have just played a game as Advent against a meduim Advent AI. After setting 4 sets of mines in 1 system and a few others in other systems I gave up making mines, I found having the extra fighter was of more benifit, and the AI must of as well. I only ever saw about 4 sets of mines trailing behind thier drone hosts and most of them were never deployed against me.
Part of the reason I did this was because after I expanded into more and more GW's I was having to make more and more hosts to lay more mines, consiquently I stopped so as to keep my fleets balanced with a roughly equal number of all different types of ships. I guess the AI was doing the same.
Now you could build heaps of hanger bays in GW's that you own to get the amount of mines that the other races can put in thier GW's, but that would take up to many tactical slots I beleive.
An idea to make this better balanced, would be if the hanger bays could build unlimitted amount of mines (150 per GW I mean). Other people may have a better idea than this but I really do think something needs to be done.
Either way I do think the Advent mines are better than they were.