Good question to be fair, and being honest I probably don't get the full value from my PC (I guess the PC components excluding peripherals probably added up to around £2k) although I think it's worth it for me.
I use my PC for some Internet and Youtube etc (although mostly do that from the sofa), General life 'admin' emails etc, some hobby video editing (having some grunt definitely makes this a much more pleasant experience Tbf) and a bit of gaming (although recently I've mostly been playing 10+ year old games!).
I use my mouse, keyboard, screen for working from home with a docked laptop (much nicer than the rubbish work provided) so they definitely get enough use to justify.
It is definitely a 'luxury' item, and I could do basically everything with a pc that cost half as much (and could still get the enjoyment of putting it together, choosing components etc which I like). However I do think it makes some of my gaming and video editing more enjoyable having a more powerful PC, so is worth it to me.
I certainly get more enjoyment out of it that I would from spending the same amount of my disposable income on fashionable clothes, a moderately nicer car (would get me a 4.5 year old second hand car rather than a 5 year old one I guess?) , expensive holiday (£1000 would get you what? 3 nights in a moderately nice hotel as opposed to spending £100 a night on somewhere perfectly reasonable that still lets you travel to and see a nice destination) etc. NB a powerful PC will last for years too, outlasting many other luxury purchases you could make imo. All comes down to personal choice.