well... the "game ending building"... is kinda your superweapons... if your opponent churns out a few novaliths... then there is a "time limit" before your economy is gone.

Although a "wonder victory"... (build insanely pricey worthless building, protect insanely pricey worthless building for X years)... would be intesting (it would also open up a game mode like "defend the wonder" where one player starts with a wonder... a starbase... a few starting labs... and 4x the resources...  and the other 9 or so players have to take it down.

I like your idea of a "pacify rebels" ablity on your envoy cruiser... and it gives you a choice... do you kill the rebels and get exp for your cap? or do you cause them to become friendly to you (and you to them) so that they will defend your planet for you... something like that would be great for multiplayer.  (if you managed to find... idk... 2 other unique ablities for advent and vasari.... this ablity would make the most sence for TEC...

Considering that armistice is a lv 6 cap ship ablity.... I dont feel fond of giving diplomatic cruisers something even more powerfull... Idk... I do think that a lv 8 diplomatic tech or 2 should be in order... and it could be something like this.

I like the idea of hiring pirates... but it would have to be very costly compared to building a fleet to be balanced.

Or just a plain "nice planet, I'll buy it" option.

I agree.

Sins would benefit from taking a look at the Civilization series (actually, I would bet they already did). There's a reason Civilization is valued as one of the best and most famous games of all time. In Civilization IV, there are six or seven different ways to win of which only two are conquest-orientated. Of course, though, capturing more territory will make it easier to achieve the other goals, as well, and vice versa.

In Sins, a non-combat victory is nigh impossible. Having culture or a strong economy helps but ultimately, its only purpose is to fuel the war machine. It doesn't work in itself.

Sins has the opportunity of becoming the real-time, more action-orientated (and frankly, more interesting) version of Civ. The roots are already there, with the GalCiv series from StarDock. It is clear that the developers were already aiming for this to some degree but I don't think they went far enough - for example, it's just too easy to counter a cultural encroachment strategy. The whole 'culture-based soft warfare' concept could be highly interesting but it would require it be made more powerful. Having superior culture is one of the ways to win in Civ, as well.

Perhaps I should just list the victory options available in Civilization IV to show just how close it comes to being what the original poster (and many others, obviously) are requesting. It should be noted the Civ has many other interesting concepts that could be adopted, some of which already are (the vassal state concept to name one). The victory conditions in Civ are:

Conquest: Eliminate all enemies

Domination: Control a majority of the world's population & territory

Cultural: Three cities with 'legendary' culture

Diplomatic: Being elected leader of a world government (which typically requires good relations to other players or simply sheer map dominance to force it through. This is the option that's supposedly being added with the Diplomacy expansion)

Space race: 1st to launch space ship to Alpha Centauri. This is the economic win as building the ship is very expensive

Score victory: If no other condition is met after the game ends (Civ is turn based with a ~500 turn limit per game), the highest scoring player wins.