Wheels make a very small difference in the performance of the bike.

Under absolutely optimal conditions, including the rider in the optimal position, a consistent wind, and cranking out 300 watts (which most people don't do), a top-of-the-line $2500ish wheel would save you 15 watts over a typical wheel. That translates to a difference of 23.3mph vs 24mph, or completing a 40k TT about 2 minutes faster. In the real world, the performance advantages are probably half that.

There is a small percentage of people who do genuinely need that advantage. There's a lot more people who believe they need it, but don't. For the average cyclist, it doesn't make a difference.