It isn't a simple yes-no question. They are worth it if you need a high quality glass. They are worth it if you enjoy looking through your scope or need to look through your scope for extended periods of time. Most folks probably don't shoot exceptionally long range or care too much about the difference in a function scope sight picture and a beautiful scope sight picture. I have a $1200 Leupold scope that still manages to impress me every time I use it, especially if I get a chance to look through a cheap scope during the same trip.
I also have a $300 Super Sniper scope that is functionally a great scope that I have used on several guns and shot well out to 1000 yards, but there is a marked difference in the quality of the image. Both are well built scopes, but the glass in the Leupold is superb compared to the SS.
It is easier to properly identify targets when looking for a specific target when the glass is better. Or, it is easier to place a shot more precisely on a busy patterned target when the glass is really good.
If you are hunting deer at 25-150 yards, you probably don't 'need' a scope that costs you a grand and can get by with a $100-200 scoope just fine. There is nothing wrong with that. However, if you are trying to count points at 300 yards, you might want the better scope.
As ever, each of the high end brands make some scopes that may not be fully amazing. It is best to do as much side-by-side comparison as you can when buying to find out which really looks best to you.
"If you look through your scope and see your shoe, aim higher."
-- said to me by my 11 year old daughter before going out for hogs 8/13/2011