Seattle? It probably was not insulated. That was back when electricity was about $0.005/kwh. When I first lived there, they sent out bills every other month because they were so low that it was not cost effective to send them every month.

Sure, you can blow in insulation in the outside walls. Or spray foam.

So it was cool on a hot day. How cold is it going to be on a cold day?

Attic is far more important than walls. As weed eluded to, insulation is far more important in the winter. The cool effect in the summer has a lot more to do with shade and windows, the coolness of the night and the thermal mass.

I'll just throw a couple of things out there. Seattle has vastly different weather than the majority of the country so you really need to check on the locals and what they do. You also still have pretty low electric rates I think. It may actually not be cost effective to blow the walls with foam. It might cost you $5000 and save just $300 a year (whether or not you find that cost effective is a topic for another discussion). Money may not be the only concern and sound abatement would improve.

You are a remodel. The tax credit for insulation expires 12/31 - don't miss it. This would certainly count.

The walls aren't nearly as important as the attic, as stated above. Insulation can be blown into the walls either through the drywall, or through the siding, but you need to really pencil out the numbers. It might be more worthwhile to load up the attic to at least R30, since the cost of blown insulation in an attic is usually really very low.

In my area, r30 cellulose cost less than $.50 sq/ft installed, and pays back quickly both in comfort and in energy savings.

I've seen foam in older homes..mostly white gritty
dust and few lumps of foam that disintergrate when you touch them. Don't have a clue what the mixture was back
then or what caused it to fail..but I have seen it
a few times.

before you insulate the attic...seal air leaks
between living space below and attic. look for
light from living space and dirty insulation
for air leak indicators.
once air movement between attic and living space
is reduced the new insulation will perform much
better.
also if your ductwork is in the attic..inspect
and seal it before insulation ins installed,

once you have done all the sealing work..then
insulate.
attic insulation is a fast payback and is the first
area you want to insulate.

always air seal first..

best of luck,

Thanks for the feedback. It sounds like loading up on the attic insulation is the best way to start. I think we'll hire some pros, so they can seal the air leaks, too. I have a feeling they would do a much better job than we could!