I'm a HUGE supporter of congregated gifted programming. But I think it's impossible to compare a gifted program in one district with a gifted program in another. We actually have several different varieties in our district.
The first gifted program my daughter attended was in Grade 1. It was purely based on IQ score, and the cut off was very high (99.95th percentile or higher). It was never intended to be a class for "high achievers". It was designed as a special education resource for children at risk.
As one teacher put it, "You know that kid who is the only one in the middle of a crowd who can't stop wiggling, and talking, and waving their arms around? Now imagine having a whole classroom full of these children!" The energy levels were extreme, and in general a studious child would not do well.
Not to mention, the teachers were not allowed to accelerate their students at all or give them advanced work. They had to stay on track with the curriculum. So that first year the teacher didn't teach math - she gave the kids puzzles and challenged them to create their own games instead. Other courses were similar. They taught the kids to play recorder instead of teaching them to read. The main benefit for my daughter wasn't educational, it was social. That, and having teachers who understood that she wasn't ADD or hyperactive or a freak.
The second gifted program my daughter was in was also score based, but the cut off was much lower. It was just 95th percentile or higher, and this score could be earned on achievement tests as well as on IQ tests. As a result, my daughter found herself in a class full of high achieving, seriously academically driven Asian kids. (There was one year when she was actually the only little white girl in the class.)
It was a different experience, better in some ways, worse in others. The advantage to being in a class of high achievers is that there's a culture of excellence. That's good for my slacker kid!

The disadvantage is that it's harder for her to find "like minds" than it was in her first program. She didn't have a friend for the first few years, though she wasn't disliked by anyone. She just wasn't interested in the same things they were. In grade 5, her classmates wanted to play tag at recess. My daughter wanted to talk about the books she was reading. She was lonely for a few years.
I think our high school gifted program is the best yet. There's still that group drive to achieve, but it's easier to find friends with similar interests. There's so many great clubs and activities! Basically, so far, high school seems to blend the strongest aspects of both programs.
So, I can't speak to ALL gifted programs everywhere. I think the ones we have served (and continue to serve) us well. I imagine it's not so good in other school districts, though.
(Gifted/LD is another issue altogether!)