I wandered into a LBS at the right time a few days back just as a customer was taking delivery of a high end carbon Trek Madone 5.7 with Ultegra components. The customer had elected to upgrade the stock wheels to something exotic and expensive prior to delivery and I ended up with the unused stock Bontrager Race Lite wheelset for $200. They are a definite upgrade from my stock wheels.
When taking my original wheels off my bike, I weighed them sans tires. The front weighs a heavy 930 grams but the Bontrager weighs about 700, a huge improvement but still not exactly a lightweight. The way I look at it is that I got the 1st 230 gram reduction for only $200, the next 200 grams will cost about $2000. I might stand pat for a while.
I rode with the Bontragers today on a hilly ride by local standards and found that I'm certain I detected an advantage but it was within my normal day to day variability. They were more comfortable though.
Neither my riding ability or current financial situation (retired) has me spending $1 to $2 thousand on wheels.