I was going through the Ancients videos, and had some ideas about the Ancients' culture.
First, I believe they advanced their technology slowly, from the line "For thousands of years our empire expanded...for so long we could imagine ourselves alone in the universe." This may have been the result of few or no wars amongst themselves, meaning less need for the advancing of technology. Additionally, it is said they retreated back to their home systems, which may mean that they took several nearby systems before discovering subspace.
It is also very likely that they did not have an extremely powerful navy, despite taking several galaxies, as they were not able to resist the Shivans very well, despite holding so much area. Though having their fleet spread thinly is a possibility, the monologues hint that they were not able to destroy fighters or capital ships-possibly due to the shields on Shivan craft.
What I personally think the Ancients were was a race of scholars rather than warriors, conquering races only for the resources on their planets.
The Shivans seem to be the exact reverse. They did not take resources in Freespace 1, and the only resourcing we saw the Shivans doing were using "Mining" vessels-which may or may not be true (misidentification by Terran command of support vessels, anyone?). This may have been the reason behind the Shivan attacks on the Ancients.
Oddly enough, the Shivans appear to advance as slowly or slower than the Ancients. In the thousands of years between the Shivans attacking the Ancients and them attacking the Terrans, little advances have been made with drive systems or subspace drives. Indeed, they seem to have done little to advance technologically between their attack on the Ancients' empire and the Terrans/Vasudans, as they were apparently able to traverse galaxies at the time of their attack on the Ancients.
Another interesting possibility is that the Ancients were actually a coalition of species, or two species working together-possibly the Vasudans. This conclusion is entirely possible, as the Vasudans seem to have had contact with the Ancients in the past, and their planet had few natural resources. It may be that their past association with the Ancients was forgotten, and their planet's resource-depleted condition a result of their first expeditions into space and contact with the Ancients.