It's not at all foolish if they want to preserve their historic wood and will pay you to do it. After all, its their wood and their project.
It is possible to do wood-epoxy repairs that are as effective and durable as part replacement.
I often let the owner make the decision to repair or replace window parts. I will cost it out both ways, wood-epoxy repair of the stiles, and wood part replacement of the stiles. It is sometimes an economic decision and the owner will select the lowest cost. It is sometimes a philosophical decision and they will want repair rather than replacement without regard to cost. Depending on the conditions and situation wood-epoxy repairs might cost more or less than part replacement. If it's an important historic site and funding is available, they may even be willing to pay more to save every fiber of remaining wood.
For more on wood window repairs you may want to consider my Save Your Wood Windows training session coming up in May:
http://www.historichomeworks.com/hhw/education/seminars.htm#HHWWindowswhere I'll be demonstrating the use of ConServ epoxies in window repairs.
John Leeke
by hammer and hand great works do stand
www.HistoricHomeWorks.com