Ground Up new Construction Lessons learned?

Our West coast projects we have to hunt for indian burial grounds ( this is CA specific) on one project we found one .

The grounds (patio, etc.) were usable but unkempt.

Which the house was condemned and was easy to demo to ground level and build back which would have know mortgage and allow us to save for two more properties cash.

For drain lines buried in the ground, which are expensive to dig up and replace, why would I dig up a 50 year old line to replace it when it might literally last another 100 years!

Thanks everyone,AnthonyYou need someone on the ground in CO to help you if it's needed.

What does that middle ground look like for you?         

HVAC duct work insulation is also deteriorated.No vapor barriers installed eitherSome fungi/mold growth notedPlumbingMultiple small leaks under sinks and from bathtub and toilets.House has Polybutylene plastic plumbing which is dangerousMain shut off valve is damagedElecticalSome small exposed wiring and bad splicing.Whole house has no GFCI's or grounding outletsInteriorMoisture spots on ceilingExteriorLose Vinyl SidingDoor Jams and Window trim have moisture damageDriveway need replacementRoofingMinor leaks noted in atticRecommended to replace roof covering, but not whole roofSome fungi growth noted in roofSo some of the question I am trying to tackle with this work is:How much should I budget for the main issues listed? 

If you need assistance with eyes on the ground, resources or companies to work with, my suggestion would be to get on here and be transparent just like you were with this post. 

No matter what you do, you cannot replace the value of boots on the ground so the next best thing(in our experience) is spend some time down there, interview some potential handymen etc. and forge a relationship, we have multiple that we have connected with in person and when you make a personal connection with them they will take care of your property better, especially in an emergency situation.