The cost of every project is site specific. In general the important things to remember is that: It is almost always cheaper to repair than replace, Plaster has a much longer life span and track record than gypsum wall board, Anything you replace original plaster with will not be as durable, last as long, or have a longer track record. As long as the plaster is up its cheaper to repair. Ask any real estate agent if a house is worth more with plaster or sheetrock. That being said there is always the exception to the rule.