1) Technology - How does technology influence governance, bureaucracy and administration? (e-democracy? where is e-democracy?)
2) Interstellar scope - How can a single Senate control hundreds of worlds, with differing ecologies and stellar anomalies each? (answer: decentralization)
But the problem is, is that whenever you have PF about the Senate, it just lumps in RL terms that are currently used in RL Senates. How the hell does a welfare system exist for an empire that is decentralized over hundreds of worlds? Was there any consideration for how a planet with a greater likelihood of natural disasters will require welfare support? How does this 'welfare system' even work? Is it by planet, or by individual? If it's the latter case, good luck getting in touch with disconnected colonies.
Now then, in Eve, you have entities covering hundreds of planets, with their own ecologies, traditions, social specificities, etc. Be it the Gallente Federation, the Caldari State, the Minmatar Republic, or the Amarr Empire, they are far, far from being monolithic. This is not even possible in terms of realism unless EVERY citizen of each is able to instantly "teleport" himself/herself on any planet of their choice, in any location they want, thus being able to constantly live with EVERY other citizen. This is not possible. There is huge gaps between planets, and even regions on planets, even with technology. Everything we read in the PF indicates that most people live in their colonies/cities/whatever without traveling on an everyday basis. The average mannar citizen does not visit Intaki everyday. What technology allows is for culture to spread and be shared (quafe being everywhere, that kind of things...), but geographical barriers remain very present and as long as people are not omnipresent and capable of interacting with everyone constantly, you can not get any kind of uniformity.
That said, you will have a colossal variety of people and cultures in the Federation, not even on the planet level, but on the planetary regional level. We all know how the Federation is about this huge melting pot of cultures and mindsets. But for the other 3 ? This is more or less the same, even if in a less exagerated fashion (and for that I am not even sure). The Republic has its seven tribes, each of them with their culture and ideals, each of them with their countless subtribes, each of them with their countless clans. The expactable variety is huge here too. The Empire maybe share something totally monolithic and uniform which is the Scriptures, but other than that, it is a terrible administrative maze based on a big pyramidal social structure, going from the slave to the main Holders and the Empress. They have almost nothing in comon (Scriptures excepted). Even Holders are all very various and different, depending if you take a Holder of a central world or a Holder at the deep end of Aridia. They all have their own local laws, traditions, etc. Considering the huge power each Holder has at his disposal, I would be tempted to say that every land in the Empire has to be totally different from its neighbors. Then, the Caldari State. Probably the nation with the less variety, and yet, you still have different bloodlines and different megas, with their own different rules and traditions.
Maybe there is a huge technological factor to take in account - and there is definitly one, how could such entities be able to remain coherent and not collapse without technological support ? - but the thing is that the Senate you refer to has nothing to do with the RL senates we know. This is 4 or 5 layers above. Take the USA or more specifically, the EU : they are already a layer above the usual nations. For now, we are stuck here and trying to build that layer. Then in the future, maybe will we see another layer appearing that will be more planetary than regional as it currently is, who knows. In Eve, they have regional layers (subtribes, Holders, megas subsidiaries, etc), then planetary layers (governors, planetary administrations, etc), then sometimes space regional layers, but eventually the upper layer that are each of the 4 entities. This is very hard to concieve. What is discussed in the gallente Senate ? What is discussed in a local planetary senate ? Probably not the same things at all.
Technology maybe tends to reduce the scale factor and erase geographical barriers, so maybe in Eve we have less very local layers like earth-like nations, but at the same time we gain several other layers put on top of all this. This is the logical step to do. Our RL ancestors 15000 years back had nothing but their little clan/family as an upper layer. Nowadays, we have our families, then our ethnicity, then our nation, and then sometimes a group of nations sharing the same principles. What will it be in the future ? Probably even more layers, while the layer at the bottom get less and less important eventually (or not...).