I think you are probably right about that. And I think that this is one of the most important differences between playing one civ and two civs. Playing two civs will require alot more effort/work than playing one.
Also, putting in more effort does not ONLY benefit you if we play two civs. The team that puts more effort into the game will have an advantage, no matter whether we play one civ or two. Its just that with two civs, getting to MORE effort will be tougher than what it would take with one.
Another thing is, that we dont control how much effort it will take to be putting in more than the other teams. They control that, because to be doing more, our effort has to be higher than theirs. The more they do, the more we have to do to stay ahead. What makes it a little tougher, is that since Sirius already practiced playing with two teams, they will be able to accomplish more with less time/effort, because they already know what to do. That means that even if we are spending as much time as they are, we will not be doing as well.
Since most of your disagreements centered around this, I wanted to make sure we were on the same page about it.
With 2 civs, the first turn will go something like this:
1. Turnplayer logs into Civ 1, Settles new city, moves warrior, selects first thing to build, checks the city window, chooses a tech, takes some screenshots, logs out
2. Turnplayer logs into Civ 2, Settles new city, moves warrior, selects first thing to build, checks the city window, chooses a tech, takes some screenshots, logs out
If the first step takes 5 mins for Civ 1 then it will take 10mins for 2 civs. At the end, you will have two cities. It will be this way for the whole game. You will be running two fully grown civs, not 2 smaller ones. Both cities will need defenses, granaries, forges, etc... I'm not sure why you think that the 2 civs will be smaller

They will be 2 regular sized civs... and they will therefore take twice as long to run as one civ... Unless I completely missed something.
I think you might want to ask about that in the "Double Civ" thread if you are still a little unsure about this.
You are right that
some threads can be combined, but Click on the "Team Kazakhstan link in my sig, and check out the Kazakhstan turn log for example. Even if you combine the turn log for the two civs, you will still have to take two sets of screen shots, and write up what you did for each team, so two write ups, which will take twice as long.