The value is mostly in hanging out with various people. The best experience has generally been when I went alone and met loads of new people, instead of going with coworkers or friends and then just hang out with them. Not that's not fun either, but I can do that next weekend anyway.
The more professionally organised ones don't tend to have that many stands, except for paying sponsors. I understand why they do that, but I think there's good value in "community stands" too.
I mean, the talks themselves are just "shut up and listen", right? Not too much socializing happening there. I think that revolving the entire conference around presentations is probably not always the best format.
There was a big space for vendors to have stalls but if you talked to them it was like talking to a sales person. Sometimes they had a tech-oriented sales person but it was still selling you their product.
So I think that repeated talks and intro talks are to be expected. Through I did not mind them, I used them to get idea about new thing X while I have time set aside for learning.
Most tech events don't in general pay for speakers or any travel. (Keynotes, scholarships, etc. are among the sometimes exceptions.)
I rarely literally re-use a presentation slide for slide but many presentations I give are based on an earlier presentation I gave. In most cases, a different conference is going to be a mostly different audience. In general, it doesn't make a lot of sense to just dump a presentation because I gave it once to a couple hundred peop,e.
Then I was looking at other conferences lineups and saw many repeat speakers from that same conf, often with the same talk, turned me off quite a bit from going to any more conferences, lots of the same, basic content, with not much expertise behind it.