Nal,
I recently had gallbladder surgery, and like you I wasn't sure if it would help all of my abdominal problems. Unlike you I had a large gallstone, and never had the Hida scan done, but when it was removed it showed signs of being chronically diseased, so it definitely needed to come out. I'm still experiencing the same problems of abdominal pains and cramping, etc., so all my issues didn't disappear when my gallbladder did, but if I didn't have it removed it could have become a much bigger issue down the road.
Your gallbladder isn't functioning properly, so it should definitely come out. It may or may not alleviate your symptoms-but you'd probably be better off without it in the long run. I was afraid that my intestinal problems would get worse afterwards (diarrhea), but it was bad to begin with so I don't know that it's really changed anything.
Anyways, good luck Friday. Try not to stress about having surgery-I've had 3 surgeries just this year and have come out just fine from each, I'm sure you will too

. The hardest part about any surgery is the recovery-take it easy for at least a week afterwards.
Everyone here has given you some great advice, and I really don't have anything to add to it other than to express my own wishes for a successful surgery and speedy recovery for you! Let us know how you're doing.