The thing with TXF is that we all know what it's about, so no matter what changes they put in place, the public already know whether or not it's something they want to watch. TXF was a bit of a rarity back in the day, in that it's audience grew series on series for a few years.
I think it helped when they started finding credible artists, but when the audience can see Syco ultimately screws then over then it all becomes a bit contrived and you're no longer watching to see who will become 'the next big thing' in music (as Leona, Alexandra and a few others had big potential to be. 1D I'm not including because I don't think anyone saw how big they would actually become from their time on the show).
When Cheryl joined, she brought a lot of media attention and a lot of new viewers. Whatever the reason, Dannii, Simon, Cheryl and Louis were the golden era of the show but I think it helped that they actually had some strong contestants too. Their fighting and squabbling made for great TV.
The problems started when Simon thought he could leave the show for the US. You don't walk out of the biggest show on TV and for the public to be on board with that. The show is so much about the judges because that familiarality is important - we don't want to feel like we're watching second choice or second rate judges.
Simon is too concerned about making the show appeal to the youth market now too. Yes they buy records, but you need names in there that work for the parents as much as the kids - Nick Grimshaw and Rita were completely wrong because Rita's had 1 album and Nick is just a radio presenter on a station that thinks you're basically dead if you're over 25.
This year will be Cheryl. Simon, Rita (confirmed there's talks with both XF and TV) and a member of 1D. I'd love Liam to join because there's never been a publicly known couple on the judging panel here (though Dannii and Simon were certainly doing it), and if they break up I can't even begin to consider the dramas
Girls Aloud: Only 5 years until their 20th anniversary reunion tour! (and only 5 years until I can change my signature...)