I recently upgraded my system after many years sticking with my old laptop. My compile times went from 10+ minutes to <3 mins simply because of a memory upgrade from 8GB to 32GB. Then I switched to the new include system and now I am down to a few seconds per compile. I can actually do stuff now rather than wasting 10mins everytime I made a few changes. A fresh engine source compile on my old system took ~2hrs, on the new one around 40mins. Again mostly due to the RAM difference followed by cpu
These increases are due to the fact that my new system does not rely on virtual memory anymore. The disk is not constantly being thrashed. Everything is faster!
What component you need to prioritize depends on your use case. For me it is definitely the RAM that has helped the most. For <i>my case only</i> I would prioritize ram > cpu > gpu > ssd in that order.
You need a whole new System. But if you are on a budget I’d suggest you get 16/24GB ram and a new gpu you don’t need an overpriced behemoth for a gpu just something recent. Remember you want to develop games not indulge in FPS benchmarking.
Don’t get the ram upgrade if you intend to replace you whole system in the near future. Any ram you get is unlikely to be reuseable in a brand new computer, it would go to waste.