I think my favorite set of victory conditions were from the old computer games Stars! (yes, the title has a ! in it). Here is a screenshot I just pulled from that game:

In that game, you had these seven different victory conditions that you could turn on and off, with a requirement that a player had to meet X of them to win. And you could specify a minimum number of years (turns) that had to pass before victory could be declared.
Looking at these victory conditions:
Owns X% of all planets. This translates into VBAM pretty well. This would be owning a % of systems on the map. It doesn't work for floating maps, but that isn't really a concern. It would also be made a static value, like 10 x # of players.
Attains Tech X in Y fields. Stars! had (IIRC) 8 different fields of technology, ranging from 0 to 26 in each. VBAM doesn't have anything like that, so if this was a victory condition it would have to be a Tech Year target.
Exceeds a score of X. VBAM doesn't have a score system, but this would be something like Census.
Exceeds second player score by X%. This is basically a runaway winner test. If you're twice as strong as the next opponent, then you're probably cruising to victory anyway.
Has a production capacity of X thousand. This would be your total system output, definitely.
Owns X capital ships. In Stars!, ships over a certain combat point value were classed as capital ships. You could therefore make owning a certain number of them a victory condition. For VBAM, I'd say this would say a battleship would be battlecruiser (CB) or larger.
Has the highest score after X years. This is a time victory. If you have the highest "score" after the deadline, you have fulfilled the victory condition.
Now, I could see something like this applied to VBAM as the basic set of victory conditions, and then the players can choose which victory conditions apply and how many of them have to be met to win the game.
Anyone else have any good ideas or suggestions for victory conditions in the base game?