I honestly think it's 1:1 Robert Downey Jr. is between 5'4" and 5'6" (from reports). I've seen the real armor at Comicon and photographed it up close, it looked small/short and was on a raised base 1-2" off the ground. I'm 5'10" and my head would fit in the Sideshow bust (but it would be tight).
On value...if you're lucky to get one of these with no damage. I think you'll be very happy with the piece. It's really cool, mine is on my desk at work and everyone here loves it. Now, I think the price tag is a bit steep for the paint job, quality control issues, and finishing work on some areas (including the base) that made the prototype look better than what we're getting. All that said, I don't regret buying it at all.
It was mastered at Stan Winston Studios (which no longer exists) from studio molds of the real suit, it's an incredible design, no one has made a replica that accurately captures the shape, expression, and character we see on screen yet (perhaps someone will eventually now that this can be closely studies). All that makes me very happy to own this piece.
I agree, if it was $499 it would be perfect.