I've never seen people come to see a cast other than other cast members.
ROFL. That's a sweeping statement. People go to Rocky for a wide variety of reasons. Whenever I'm going on a road trip to Dallas, Fort Worth, Houston, San Antonio, Corpus Christi, etc. it's certainly because I want to see the cast there. There wouldn't be much point in driving three hours each way if I just wanted to yell lines in a different theater.
You say you were there for "the people", and what is the cast but the backbone of "the people" at most theaters? Generally speaking (and Billy Joe's is an obvious exception here) if there were no cast, then there would not be a critical mass of people and the show would die. I've seen this happen multiple times when a cast disintegrated for whatever reason, and not long afterward the theatre would stop showing Rocky at all since the audience disappeared with them.
and not to see a cast do exactly as they are doing on the screen
That's obviously going to depend a LOT on the specific cast. I've seen shows that emphasized T&A above all things, and shows that were obviously just a group of friends fucking around who didn't really care about the audience at all (an easy way to tell this is when the "show" is mostly just a long series of inside jokes). If I'm visiting Houston, I have two different casts to choose from. One is going to lean more towards the screen accuracy side of things, while the other is going to lean more toward the 'Hey check out this girl's tits!' side. I've enjoyed both at different times.
You can't hear a word of the movie these days and everyone is so damn eager to yell over everyone else that it makes the AP strained, forced, and incoherent.
That's one of the more frequent complaints from people that saw Rocky Horror back in its heyday, and are now taking their kids to see it. "It's nothing like it used to be!", they cry. "Everyone's yelling something different!". And that's certainly true. Rocky Horror Show stage performances have to struggle with this issue as well.
But what are you going to do about it? Tell the people yelling the 'wrong' lines to shut up? Inform the audience that only previously approved line callers should shout anything? Hand out scripts with the accepted local lines? Sure, if call lines are yelled in scripted unison then it would probably be a better experience for virgins. But the show as a whole would obviously lose out on the creative chaos aspect of Rocky Horror.