Worth is a subjective question. Relative worth may be easier to deal with. I always ask the question "if i have $1000 to spend, where do i get the biggest benefit". That depends, basically, on where the biggest problems are. And its exactly why i'm leery of most expensive tweeks, including cables and similar doo-dads.
Speakers traditionally have the greatest compromises. Unfortunately you need not only money but tolerance for size to move up with speakers.
IMO sources (turntables with carts) and DACs are also ripe for improvement. And both are fairly complex so it make sense. As i work on DAC designs, the number of small to medium pitfalls is large. power. grounding. Isolation. Filtering. Blah, blah. never-ending.
The best amps and pre-amps ought to be nearing perfection. nearing, not there. Sadly, many are not. But the declining marginal returns are in full force over $2k for pre-amps IMO. Amps are more complex to answer since some speakers, in some rooms demand lots of power - and power you buy by the pound to a degree (transformers, output devices, heat sinks, and a chassis to hold all that heavy stuff!)
Right now i have a prototype integrated making the rounds. Its ~ 40w/ch/8 ohms and is targeted to sell for $2000-2500 "depending". It has qualities where it is superior to and others where it is slightly inferior to, $7-11k worth of separates.
Now, nothing i design will "wow" anybody with lots of seductive distortion. That's not my thing. I want it to disappear, erring toward "never be obnoxious". So if what you want is a ton of euphonic harmonics, go for it, but that's a 'whole different kettle of fish.
But the best answer is - listen and trust your ears. As a great sommelier once told me when i asked the best way to really learn about wine: "pop a lot of corks".