For the boat in question I would say that it is well worth the cost of the restore. I did a rebuild almost the same as that you are querying. Local shipwright estimated about 3 months work for a full time employee. I used thermolite as much as I could. Some of the extra costs for the material are absorbed by less labour costs, increased re sale and also the knowledge that nothing is going to absorb water or rot. Its also stronger the the equivelant weight plywood or whatever wood is being used.. The shipwright I used to assist me quotes all his jobs using thermolite and yes he does lose some business because of the extra cost but those who decide to spend the extra are extremely satisfied with the result. Just a simple example of my experience is something as simple as drilling a hole through a transome for cables in thermolight is a 2 minute job as nothing needs to be re sealed. Compare that with a plywood transom where you drill the hole and then spend the time to re-seal the hole with glass and hope that it is 100% water tight. The shipwright I worked with is only too happy to have someone do as much of the removal as they can before bringing the job to him.. Just make sure you take into account the fact that you are going to have to spend the money on repairing the boat when deciding how much you should pay for a boat. Do your research on finding a good shipwright to do the repairs as they have different qualifications to someone that does firbreglass repairs.