Bathroom Renovation - Remove Plaster Walls?

Remove all walls, replace branch lines back to riser, install Durock, waterproofing and tile

Make sure they don't just use greenboard.

You definitely remove the walls. The last thing you want to do in undertake the most expensive room to renovate and put in a lot of lovely finishes only to have to tear it all up when you learn there iis a leak in an ancient pipe in the wall or an electrical short from old wires. Aside from preventative benefits, you gain the possibility of adding electrical outlets and lighting options, increasing water flow with slightly larger pipes which is possible in some situations, and installing wall materials that will resist mildew and issues generated by a steamy environment. If all you were doing was replacing the sink and toilet and vanity light, then leaving all else alone could be up for discussion. But once you start removing a tub/shower/tiles or dickering with the electrical or plumbing, bite the bullet and do a proper gut. You'll be glad you did in the long run.

Don't forget a shut off for each item. It costs more but when something goes wrong you will be able to shut off the item in question but still use the rest of the bathroom.

Great - thanks for the feedback!