I'm upset about my sisters venue choice for her rehearsal dinner
I'm curious if it upsets you this much if you're going to ask her to change the venue?
No.  But she just didn't ask me about a lot of things, and I don't want to be involved in her wedding at all
Your sister's wedding is a very important day for her, and she wants everything to be special, even if others don't share her opinions on everything.  You shouldn't be trying to manipulate her choices into things that you would like, and you should be there for her on her big day, even if you are frustrated at times.
It's her dream day, but I don't fucking care.
You should care, because like you said, this is her dream day. If on the most important day of your life, your own sister ruined it by making a fuss, would you be happy with her?