I have actually been remodeling an older home with radiant ceiling heat. This system was 220v. The heating wires were stapled to one layer of drywall then a special "mud" was used to level the ceiling surface.
First, go to great lengths to make sure that you don't damage any wires!!!
If any wire gets broken it is extremely difficult to repair and even more expensive to replace.
Any ceiling cracks can be difficult to permanetly fix. Glenn is right on product use, it's just that the ceiling heat causes a lot of expansion & contraction in the ceiling and the cracks tend to reappear when the season changes. We carefully cleaned the area, applied self-adhesive mesh drywall tape then mudded appropriately.
We found the popcorn texture on the ceiling to be a real problem. In this house, it was very diffcult to blend patched areas, was very flaky, and fell off easily. Any direct contact caused globs of texture to fall off the ceiling. We resorted to re-texturing the ceilings. First we power sanded off all the exisiting texture then used a product from Zinzer called Gardz to seal the remaining loose texture. After that, we used a good quality primer and then textured normally.
This house had very high energy bills. We found inadequate attic insulation to be the cause. Much of the heat was radiating directly into the attic rather than into the house. The duct work for their a/c was also in the attic and was poorly insulated and very leaky. The best solution was actually to insulate the rafters with foam.
"Energy Upgrades" to this type of system are probably limited to programmable thermostats. Your electrician will be able to determine the correct thermostat. If a zone fails the cheapest solution is to install baseboard heat. You can look in your breaker box to determine the voltage of the system.