I have a couple questions regarding dialogue choices in the first KotOR. The dialogue is the most interesting part of the game, imo, and I would like to understand the background workings a little better.

a) Does your class have any bearing on dialogue, after the Endar Spire level? Like, will anyone after you leave the Spire say different things if you're one class or another?

b) Do you get more dialogue options if you're character is really really Light/Dark Side? For example, if your character is all the way to the Light (or Dark) Side, will that open up new dialogue options?

c) Or is it WYSIWYG, and you always get the same options to pick from no matter what?

Class, only in one dialogue option with Carth and Bastila. Alignment, still almost never. It really all depends on what you feel like clicking. The only time you'll get multiple aspects to conversations (and how the game plays out too) is near the end when you decide to whether to go completely light or dark.

So no matter what kind of character you are, you always have the same options to click from? (i.e. there aren't any hidden options that will magically appear for you to choose if you play a different character)

Nope.

Playing a different class would not affact your dialogue options.

Playing DS/LS would cause minor difference. Basically a couple of LS options would not show if you are really DS towards the end of the game. And yes people would comment on your LS/DS-ness. Other than that there is little effect. So yes you can go completely LS and get the DS ending with almost LS alignment if you play your cards right.

The only time I can remember that I've seen completely LS or DS options that weren't near the end of the game was on Nar Shaddaa in K2 at the very beginning of the planet, when the beggars are asking you for money, and then Kreia has a discussion with you about your actions. But that obviously isn't in K1, so it doesn't pertain to this thread.

As Emperor Devon said, class only affects two things, one in a conversation with Carth and one with Bastila. Both times they are asking about your background, and only pertain to your first class, not your Jedi class. For Carth, there's a difference between what his says in response to your answer if your class is scoundrel instead of soldier or scout. Basically, he just is a bit suspicious about your background as a "smuggler"- but it doesn't actually effect gameplay. For Bastila the response is the same no matter what class you are.

As for alignment- well, certainly your actions affect dialogue. For example, if you kill Juhani instead of convincing her to return to the Jedi, the Council chastises you instead of congratulating you when you return. Basically any quest has different turns in dialogue if you do the Dark Side resolution, Light Side resolution, or neutral resolution.

As for if your general alignment affects anything- as far as I know, only conversations with some party members are affected. The biggest affect is that it's basically impossible to do the romance with Carth if you are a dark side female.

Well, in the very first dialogue there are 3 different options depending on your class (when Ulgo tells you to go find Bastila).

There are? What's the difference? (Of course, since it's the very beginning of the game, I could easily find out myself, but I'm lazy)

Also there's some hidden dialogue that you can unlock with a mod. Juhani for example will ask about you and comment on you being a soldier.

There are? What's the difference? (Of course, since it's the very beginning of the game, I could easily find out myself, but I'm lazy)
Ulgo says something about your past to give the player some background. He says something like, "I know you were a great smuggler/explorer/soldier, your reputation precedes you..." - stuff like that.

But I already knew about that one, I was asking for instances after the Endar Spire.

As for if your general alignment affects anything- as far as I know, only conversations with some party members are affected. The biggest affect is that it's basically impossible to do the romance with Carth if you are a dark side female.
Are Carth and Bastila (and their romance options) the only characters that are affected by alignment?

Also there's some hidden dialogue that you can unlock with a mod. Juhani for example will ask about you and comment on you being a soldier.
Could you tell me which mod? It sounds interesting; I wanna check it out!