Personally I continued to find new dialogue in KOTOR 1 in my 5th play through, however playing KOTOR2 again, and again I'm not sure if I managed to hear it all or if there is still some out there that I somehow missed. If people could post a list of dialogue they encountered with their NPcs I would be grateful. 
  
If this is a repeat topic and had been discussed previously could you please post a link to said topic. 
  
 To make things easier I won't count cut scenes or the discussions from defending Telos and Malacor V 
  
Off the top of my head I can only think of: 
  
Krea 
*Beginning conversation 
  
*what happened after the Mandalorian wars eg. a vague explanation of what happened during the Malak/Revan Sith Wars 
  
*what she knows of the sith threat 
  
*Did she know Atris/why don't the Jedi recognise her 
  
*"I want to know more about the force"-question 
   - The bond 
   - build a lightsaber 
   - lightsaber forms 
   - force forms 
  
if you are light side then you get quite a few 'why bother helping people' lectures such as: 
  
*why do you act with mercy 
  
*if you help people it can only aid in weakening them 
  
*Revan and how she was his/her mentor 
  
*after you battle Visas: the conversation about sight 
  
if you save Visas 
*the conversation regarding trust and the destruction of Visas' homeworld 
  
  
Atton 
*Beginning convo and Revan 'alignment' 
  
*comments up to the harbinger 
  
* "can you teach me to Play Pazzak" 
  -Pazzak rupublic senate rules 
  -[Play Pazzak] 
  
*Echani training 
  
*the 'Some guys told me they knew you on Nar Shadar' 
  
*the Jedi he loved and turning Atton into a Jedi 
  
*Playing Pazzak in your head 
  
  
Bao Dur 
  
*beginning coversation: Mandalorian wars and if you remembered him 
  
*where he picked up remote 
  
*what happened to his arm 
  
*what he did after the Mandalorian wars/how he ended up on Telos 
  
*Why he/you joined the Mandalorian wars 
  
*How he felt after visiting Duxin 
  
I know that there's more conversations you can have with the characters, but that's all I can think of at the moment in my sleepy state of no sleepness 
  
BTW: The way that the dialogue is structured in KOTOR2, partially due to the influence system I think, makes it more difficult to write down than the KOTR1 dialogue. Hopefully I haven't managed to confuse things further by listing them this way.