Upgraded electrical, plumbing and hvac systems as well as the structural integrity of a property are more important the the actual age of a property.

I've rehabbed properties to the studs/pulled out all electric/plumbing/hvac and rebuilt from the inside out. 

I had 11 of these and good systems in place but still had 1-2 evictions a year and 3-4 big things that were normal annoyances like plumbing leaks, damages from hurricanes, or some vandalism.

Similarly, our skills don't typically go into deep technical electrical, or entirely re-plumbing a unit.

I learned I pretty good at laying down flooring and fixing drywall but I really have no business doing plumbing.

I learned I pretty good at laying down flooring and fixing drywall but I really have no business doing plumbing.

The building is listed around 750K and the renovation budget would be around 250K (new electric, plumbing, kitchen, bathroom, windows (old ones are lead), HVAC, garage, removing lead paint, lead pipes etc...). 

I closed on a duplex a few month ago and now there is a plumbing issue where the plumber says that they'll need to change both main lines to the house and reroute the piping since it's all leaking. 

Full disclosure: I'm no professional, just giving some insight as to what our inspector discussed with us.It actually was beneficial in that the inspector could easily go under and inspect the structure, subfloor, plumbing, etc..The concerns that our inspector listed were things such as damage/rot to sub-floor,  ensure the support post/columns are structurally sound, the raised front patio is concrete and brick, but they used temporary wooden bracing in the construction but left them in place afterwards which he said provides termites a way to get to the framing of the house.

What permits cost in your area, What kind of cost a plumber will charge for a faucet or re-plumbing the whole house.