For me it basically comes down to skill. Having all those great streams to watch and learn from, you quickly realize how little of a chance you'd actually have in an official tourney.
And seeing how many of the top players are old CoH1 heroes it feels like they are simply light years ahead.
What would make me sign up for a tournament?
If there was a tournament more suited for my skill-level I'd consider it.
Prizes are not interesting actually.
My ideal tournament which i'd like to see, and participate in would;
Be a single or two day event. Mid-skill (100-500?) A dedicated team of streamers/commentators that can go through the highlights/upsets/strats etc. Just like with any other sports event. And not only entire three-game series.
And of course, being able to observe the games live as they are being played would make ALL tourneys much much more fun in every way.