Considering the victory conditions and what you should do to achieve them, I think only the Research victory is really unique.

With Research goal, you just need to figure a way to survive long enough, but there you can use different means of your choosing. Plus then you need fast research, of course. But once you get far enough victory is certain, it does not matter if the enemy is at your doorstep, you win when you just reach that one set goal.

With conquest, alliance and influence victory, it seems you can trade between the types of victory. Basically you'd want to have some real power and possibly control large portions of the galaxy. Expand and dominate.

Conquest is the most classical way, just kill everyone. But influence and alliances can be helpful tools in this task as well - use influence for the conquest when suitable to save your strenght and reap the fruits intact, and alliances whenever you need some help or just plain diplomacy when a breather is required.

With influence, it doesn't hurt to do a bit of conquest on the side, just to gain a foothold faster. Diplomacy is useful here as well. Also, you should note that if it is too hard to conquer, influence may be an alternative way to cripple your opponent.

It's a bit same with the alliance thing. If you're lacking in military or culture, maybe you can fill in with diplomacy and just ally with some of the tough guys. Or if some boneheaded civilization totally fails to grasp the concept that you want them to be your ally, just go and get back at them with your military or influence.

In other words, the 3 strategies play more or less the same, and you can switch between as circumstances develop. Or did I miss something?