Absolutely worth it. Our system uses different terms and tests than yours, but the basics are the same -- at the end of second grade, parents whose kids are eligible through testing for the Advanced Academic Program can choose whether to send their child in third grade and up to an AAP "center" school (with all advanced classes, all the time, with all other students in those classes being AAP students too) or whether to leave their child at their geographic base school (with once-weekly pull-out class for some academic challenge).
We chose to send my daughter to the AAP center, equivalent to your "talented and gifted elementary school." Best decision ever. though we liked the warmth and community of our base school; still I'm glad we made the change and she is too.
Your daughter would be among other students who operate on her academic level. The teachers can focus on developing work for these kids that is challenging to them and interesting to them (and the teachers don't have to spread themselves too thin trying to work with a classroom where the kids range widely from very academic to barely getting by, which is too often the case). All her subjects will be taught at a more challenging level -- and that will be more fun for her and she will not be bored as she likely would if she stays in her regular classroom. The pull-out weekly classes just cannot give academically what these kids get by being in classrooms that are geared all the time for AAP (or in your case, GT) learning.
Some parents say that if your kid isn't super-motivated and very driven she won't do well, but after two years in our school's AAP program, I see kids who are indeed more driven students and also those who are very mellow and not "scholars." Both types can thrive in these classrooms if the program recognizes that they're kids, have different learning styles and don't necessarily have to make all A's all the time as long as they are actually learning something interesting to them.
I would talk to her potential GT teacher or the GT school's counselor or principal and ask if they think that every kid has to be super-driven to enjoy and thrive at that school. Ask how the curriculum differs from what your daughter would get at her base school.
In our system and maybe in yours the deal is, if they test into advanced academics/GT at age 8, they are "in" for the rest of elementary school, and you could decline to send her to the GT school this year but send her the next year. Personally I would advise sending her this fall if you think she is going to go at all. Waiting only makes it harder on the child; going sooner helps the child forge friendships sooner and get used to the level of work. I knew a family that waited until sixth grade to put their daugher into the program and they really regretted that, because after five years of sailing through everything in a regular classrooom with no effort whatsoever, she suddenly had to work a little at school, whereas if she'd started in third grade, she'd have been used to being more challenged. Know that your child will be getting the same curriculum as other kids who are not in the GT school; the difference is that the curriculum in the GT school may go deeper, have more independent activities/projects, be more creative, etc.
Someone posted that you lose a lot socially by not going to the neighborhood school. But our school is just on the other side of our small community so my daughter has no social issues getting play dates etc. with her friends from her AAP school, and she keeps up with a few friends from the old school (our neighborhood school) because we make that effort. It hasn't been a social issue at all; only you know if it would be for your daughter, but frankly, I think getting the right school takes precedence over "I might lose the people who are my best buddies at age eight" or "I won't be at school with my next-door neighbor." Kids find new buddies pretty quickly at this age -- but it will be tougher if you wait to send her when she's older.
Anyway, our experience has been good. It does indeed depend on the child and I have friends who did not choose to send their kids to the AAP center school and are happy with that decision too. But for us, the challenge of the classes and the fun of being around kids who are very interested in school (and mostly who want to be there every day) has been good for my daughter.