@Nuclear: Maybe idealistic wasn't the right word. I would say, however, that she was "enthusiastic" about traveling through the galaxy and seeing news places. As an example, I believe if you talk to Tali in a certain place(s) on the Citadel, she says something about "I could get used to living like this." This suggested to me that she found the traveling exciting and a welcome departure from the Flotilla.
In contrast, she really never indicates that she likes the adventure anymore in ME2. Everything's more about the mission. This makes sense.
I'm not sure Tali was ever that much of an idealist (I'm open to evidence, of course, this is off the top of my head). She came from a pretty grungy place ("just a month ago I was on rusty old tug") and while she then got into the adventure of her life, it took her dark places, like nearly getting murdered in an alleyway. I was suggest there was a little naivety rather than idealism (again, the alley meet with Fist's goons).
As for her belief in the Migrant Fleet's political system... I don't know that she ever expresses an opinion on it in ME1. I got the impression that her father was overbearing in ME1, but nothing about the system he was part of
Maybe she doesn't. But there seems to be a stark contrast. Whereas she may not really offer an opinion about the government in ME1 rather than simply stating what they are, in ME2 when she talks about them, it's usually coupled with something negative.