I'm probably over-thinking this, but...

       According to a statement made a long time ago, Mass Effect 2 will import your save files from the original. Supposedly the decisions you made will have weight in the sequel. For example (SPOILERS) the character you let die will still be dead, and so on.
       The process of playing through the game and picking dialog options is very influential in determining how you view the story, characters, your relationships with the characters, and so on. Now on to my question.
       If I play the original a second time through, do you think it will "ruin" the story/character development of the sequel? After playing through the first time I have very specific ways in which i view every aspect of the game. I wish to retain this "familiar setting" when I play the upcoming sequel. But if I play through Mass Effect again, it seems like the process of choosing different dialog options will "reset" my original experience.
     Am I making any sense at all? What do you think?

I don't think either the most boring guy ally in the game, or the perma-PMS girl will even be in the sequel.

I played through the game 4 times and started 3 other characters I didn't finish it with.  If anything, it only strengthened the fact that I remember every event that happened in the game.  It doesn't ruin it at all.

Adding to what Shadow said, I'm fairly certain that you can choose which save file you'd like to import from specifically. Thus, you should get to choose which memories and decisions you bring with you to ME2.