National prestige.

[Aemilius Paulus]

Is this a fact, does large cities and advanced buildings actually give more respect in diplomacy? Or is it just me?

No, but the AI is less likely to be friendly to you if you are big and dangerous. That is a known fact. So if you expanded less, had less armies, or had less battles in your economically-minded campaign, then the AI was less afraid of you, leading to more efficient diplomacy. Although usually, such hunches fall into the category of "just me" as you put it. Unless you are willing to provide empirical evidence based on a great number of instances.

[Seneca]

Well, I don't think I have the patience to write down every diplomatic encounter.

However, yesterday I trained a few stacks, took Ipsos from the weak AS, and Serdike + Sigidunum from the Eleutheroi. After that I sent two stacks to sack all the ptolemaiois coastal cities and grab salamis for my self. Next thing that happens is that Rome and Phalava (the major players in respectively west and east) comes suing for alliances.

No one has deared to attack me for 30 years Except the Ptolemaioi, but I plan to become an aggresive bully in ten years time. Perhaps diplomacy will take a different turn then?

[Tollheit]

So if you expanded less, had less armies, or had less battles in your economically-minded campaign, then the AI was less afraid of you, leading to more efficient diplomacy.

I agree with that, except for "had less armies".

[Seneca]

I stand corrected. After the last post I played a couple of turns, and out of the blue my allies Pontos lays siege on Ipsos, thus betraying me and breaking my alliance with Phalava. From another point of wiew this could quite possibly be because of our bad history before the alliance and the sudden lack of a bufferstate between me and Pontos.