Martin,
It's somewhat a personal preferance.
In many areas, copper will last quite well.
In areas where copper may last less than 30 years, I would consider replacing it.
City water in the Seattle area, is good.

Deciding between a manifold system or a standard pipeing layout, is choice too.

Either way, it should be fine.
It's all about sizing. Add the numbers up and go for it.
Terry

: I'm doing major remodeling of bathrooms and kitchen in my house. I'm going from 1.5 baths to 3, ultimately and rearranging the kitchen floorplan.

: I like the idea of using PEX because I have no experience with copper. Currently the plumbing is all copper inside the walls and it seems to be in good shape.

: My question is:

: wherever there is existing copper plumbing close to new fixtures (typically with 5 feet) should I:

: divert the copper lines to the new fixture with PEX?

: divert the copper lines to the new fixture with NEW copper?

: completely redo all lines with PEX from a new manifold and using home-run circuits?

: Access is not a big problem since this is a 3-story house and most work is on the 2nd and 3rd floor. I will be removing lots of drywall and floor sheathing anyway. Most plumbing is on the 2nd floor and I have easy underfloor access from ground floor unfinished storage rooms. I was thinking of putting a new Vanguard manabloc manifold in the utility room on the ground floor.