I think if you're a professional, this was a no brainer - IMATS was an absolute cattle market and there are some brands who just won't do IMATS such as Face Atelier (they did it last year, but have opted not to this year), and Kevyn Aucoin who had unbelievably awesome show specials. It was worth going for that alone! I got to sign up as a Powder Group Pro member, and signed up to numerous pro discount programs at stands when usually I'd have to bring out all of my credentials. I had 'em with me, but still - it made life much easier. I'm not sure if Smashbox and Stila Pro would be showing at IMATS, although I doubt it, and I know that Yves Saint Laurent (who offered a 20% discount at The Makeup Show) said that they won't be doing it.
I got to take some invaluable workshops and actually managed to make connections with other professional artists, which was awesome. For me, I got so much much out of The Makeup Show than I did any of the times I went to IMATS, but maybe that's just me.