Foam insulation in existing walls - good idea?
We want to have our attic and walls insulated, and just had an estimate done by USA Insulation. They would insulate the attic by blowing in some white fluffy stuff (I think he called it encapsulated fiberglass) and fill the exterior walls with foam. He said it was low-expanding, so although it would fill the cavities, there wasn't any risk of wall damage from over-expanding foam. Our home was built in 1957 and has very little insulation. Our heating bills are through the roof (no pun intended), we heat with hot water baseboard heat and the boiler is only a few years old so it's not the problem.
Is foam in the walls a good idea? Once we do it, it's there forever, so I want to make sure it's the right choice. He quoted $4900 for our one story 2200 sf home, including the attic, walls and foundation. I'm not really asking if that is a good price; I really want to know if there are any drawbacks to the foam.
I'd like to make a decision fairly soon, so if anyone has experience with this type of insulation system, I'd love to hear about it.