"This assumes every other civilization thinks like humanity does"

Survival of the fittest is a fact of life, and whatever mindset one has about it may be irrelevant.

As game theory proves, the majority, or even all players may dislike the game, but they have to play it all the same.

"the resource allocation problem might be solved with technology"

Perhaps there are resource allocation problems that can't, eg. the scarcity of habitable planets.

"it's likely that they are by default peaceful and not aggressive, because if they were aggressive they would have stopped existing due to escalating internal conflicts aided by advanced technology"

Or it could be a bell curve with a self-destructing "war of all against all" on one side, "peaceful but defenseless monks" on another, and the middle-of-the-road compromise of "disciplined legions where backstabbing is forbidden" being best fitted for survival, preying on less efficient civilizations from both ends of the spectrum alike.

There are of course other limits that may or may not be solvable, like most of that metal being stuck in relatively deep gravity wells. But it's still an interesting thought.

Suppose you wanna conquer a civilization 1M lightyears away, but by the time you get there, the technology of the civilization will out grow yours. What's your strategy?

One can imagine a conquering civilisation though, that has peace enforced on the inside.