I have kept much older machines running for a long time, so I understand using what works.
The state of the ordinary today is so much better than the state of the art from then.
Since this is the V1 forums, I’ll note that the V1 MP3DP V5 machine is amazing.
From your list,
- PS to 24V
- new controller (say, SKR Pro 1.2)
- new build platform (24V or AC Mains, > 200 x 250mm platform)
- Upgraded, possibly new extruder.
You’re well over halfway to a completely new machine at that point.
Not mentioned, but a probable consideration is firmware. For a new build you may want to run Klipper and that may either change your controller decision or add something like a raspberrry Pi to your list.
Do you prefer to build your own? (I presume so given the nature of the question.)
Then the question is one of budget. Voron 2.x or MP3DP V5 or similar puts you in the ~$900 up to $1200 ballpark and up depending on options.
You might also want to buy and mod, like the the FlashForge3 AD5M discussed here on the forums. Budget maybe 60-70% of the build above.
Finally, if you’re considering a rebuild / mod anyway, you may consider hitting craigslist or marketplace or similar and finding a locally sourced newer platform to mod. There’s a ready supply of modern machines in the hands of folks that bought them and got bored or couldn’t keep them running. I’ve helped a few folks go this route, and it can be VERY cost effective.
Not sure I answered any of your questions but perhaps it’s at least food for more discussion.