If it's something you use for work, the time saved could be justified if you have to compile or do something CPU-heavy often
I'd love for me to be able to just run all my builds on full blast on a 24 core beast at home, but if your interests also include games, you're looking at multiple thousands just to upgrade. Needless to say, my apartment, family, vacations and a dozen other things are well above in the priority list.
* $500 for a CPU (7800X starts at $450)
* $60 for a cooler because the Wraith Prism is shit.
* $200 for a motherboard, maybe $100 if you want to try to cheap out and get something that might have unstable voltages, shit PCIe bandwidth or no NVMe slots, etc.
* $200 for 32GB of quality DDR5-4800 (or 5600 if you want to be fancy), and that's easily used up these days.
* $200 for a quality 750W power supply
* $100 for a case with good enough airflow, assuming you don't already have one.
* $200+ for at least 1TB of NVMe storage, easily much more
So, assuming a new build that didn't get incremental upgrades in the past, building a new, powerful PC these days is going to run you $1500. Without even picking any top of the line stuff. Guess what didn't get included in there ? GPUs with their bloody ridiculous prices. If you're going with NVidia, this 4000 generation is a waste if you're buying anything but the 4090. You could absolutely buy a 4080 (or rather a 4070Ti), or a 4070, but they're such a horrible deal in terms of price/performance. And that's going to cost you at the absolute least $800 (for a 4070, which is a dogshit card). Or you can try to find a series 3000, but that's also going to run you $1000+. If you're going with AMD, your problems are similar, for cards that are really subpar. As for Intel, well, let's just say an A770 with your high end CPU might cause a few bottlenecks here and there.
So, yes, if you're lucky enough to find deals _and_ to have stuff that you can still use from an old, recent rig, sure, building a new PC isn't _that_ expensive. If you have to do major upgrades, you're looking at multiple thousands. Pulling that much money out in one go for something that is ultimately not extremely necessary is something that can only be afforded by a very small percentage of people.
And if you already have an older rig… just bring it over from that.
So, no, any upgrade not done in the last 5 years means pretty much a full rebuild now. New sockets + DDR5 means that your old build is going to hit a brick wall.
Your old PSU might be insufficient for the new build, but it's not like 750W PSUs are a new thing (or particularly required if you're not doing a high-end build, even today). Power efficiency tends to yoyo around over the years.
No, you absolutely do not "need" to upgrade your GPU, and certainly not immediately. Your old GPU will not be doing a worse job in the new computer than it was in the old one. And you can always replace it later on, should the need actually arise.
I think a core part of the misunderstanding here is around expectations. The build plan for "a top-spec gaming computer" is going to look pretty different from "a top-spec dev computer that I can also game on". But, if anything, gaming has hit seriously diminishing returns in the last couple of years. It's quite hilarious and sad to see NVidia try to make real-time path tracing and 4K gaming into things, in a desperate bid to make GPU performance a relevant factor again.
The only compromise compared to the last gen is unfortunately the RAM - 64GB this gen compared to 128GB last, until they sort out DDR5 4-DIMM dual-rank configs..
So you need to be paid ~$30/h to recoup the cost in a year.
Of course if you're contractor it means you will... earn less unless you bump the price but that's the "motivation" of being paid by hour...