Suddenly, I sort of feel like Follow That Bird would have been a great time to reveal that Snuffy was real. Well, except for the fact that the movie didn't do well in theaters.
In the movie, nobody mentions the fact that the adults didn't believe in Snuffy, but that could have been a plot point.
Like, in the movie, Big Bird is initially reluctant to move away and live with a bird family, but it doesn't take too long to convince him. Perhaps there could have been more time for Big Bird to decide, he could have talked about it to his friends, leading to them making a big deal out of how he wasn't real, which could have been what caused Big Bird to finally decide to move (so that he wouldn't have to deal with their "Snuffy is imaginary" attitude anymore). It would have also been a good ironic echo later when Big Bird decides to go back to Sesame Street when the Dodos pretty much say he can't visit because he's not a bird. Maybe the adults would finally see Snuffy while Big Bird was gone, or maybe it would have been better if they'd seen him at the end after Big Bird had returned.
Or maybe it would have been better if when Big Bird was deciding on whether to move and live with a bird family, he decided to talk it over with the others, but before any of them knew what was going on, Snuffy was brought up, they made a big deal out of him being imaginary, and Big Bird decided to make his decision. Like he asked all of his friends to get together because he had something important to talk with them about, they thought they were all there, Big Bird mentions that they should wait for Snuffy, they all complain because they don't think he's real, and Big Bird gets so annoyed and emotionally hurt that he makes his decision without talking to them about it.
What I've just been talking about reminds me of a post I recently saw on the Tough Pigs forum, where somebody thought it was odd that the movie makes a big deal out of Big Bird and Snuffy being best friends yet since the adults thought he was imaginary they couldn't have Snuffy come along to search for Big Bird (even if there was no such issue, could Snuffy have fit in any of the vehicles?).