More expensive = better?

At some point some audio equipment became either Art, Or a fashon statement, or both. Your pretty $6000 speaker wire sure sounds nice. I'm sure glad I went to school to learn about such things. 

You have to compare apples to apples. Price can reflect things such as built-in DAC card, phono section and/or headphone. The casework can add extra cost (engraving, anodizing, finish, CNC artwork, etc.).  Also, if it is sold direct it's about half the price a dealer would charge. Can't really generalize an answer on a dollar for dollar basis with respect to sound quality.

always

as in, 100% percent of the time

😉

I’d humbly propose widening the lens.  Assuming legit manufacturers, etc, a $150,000 preamp+amp(s) combo will always sound better than a $5000 integrated.  It just will, even to the most jaded among us.  Sure sure, you could have your quips, but it won’t be a serious comparison.  So, in a sense, “a lot more expensive” usually does sound better.  Turning to the OP’s specifics, comparing an $8000 amp to a $5000 amp could be pretty much like comparing a Coke to a Pepsi.  (Except without the decades of history proving that Coke is better.)

I think about it in categories, just as a rough guide.  5-10k amplifiers, for example, are all on the same footing.  Use your ears.  5 v 20?  Decent chance 20 wins.  5 v 50?  I’d bet a chunk of cash that 50 wins.  

All other things being equal, intuition would suggest that an amp costing $8,000 would be better than an amp that costs $5,000.

Keep it simple.  Its not like choosing Coke or Pepsi you know.