[Greenbuilding] Foam vs. wet spray cellulose vs. "flash & batt"

[Doug Horgan]

Okay, so we're all looking into better insulation. And going energy star
with our new houses.
There seem to be two kinds of insulators around here, the all spray foam
guys, and the regular guys who now dabble in spray foam. (Around here
being Washington DC, climate zone 4, 4000 HDD & 1200 CDD).
The spray foam guys say if you use all foam you will save so much money
your electric meter will run backwards and automatically fill up your
bank account. (I think that's what he said, it was a lot like that
anyway...). Seriously, 500-60% savings vs. "normal". This for R15 walls
& R25 attics.
The other guys say to "flash and batt": use 1" foam at the most, then
batts or cellulose. They claim the foam gives you all the air sealing,
and you don't need to spend money on more foam after that. It is cheaper
by a bunch, like 20% less than all foam.
And, we have a gentleman working for us who's from Michigan and says
they only ever used wet-spray cellulose up there and he isn't sure why
we'd use foam at all.
So: 
1. Does 3-8" foam really do much more for you than other insulation?
2. Any thoughts on flash & batt? Specifically, how does it do on air
sealing? Anyone out there who has done blower door tests on houses
insulated that way?
3. Can wet spray get the job done? Again, anyone know what to expect
from the blower door when you do good air sealing and wet spray?
4. For that matter, can you get a good blower door score using batts?
Around here we never use a poly interior vapor barrier/air barrier,
because of our high cooling load, but I have been reading up on sealing
rim joists, bottom plates, using a bead of glue around the entire
perimeter of the drywall, etc. etc.--does this stuff ever get you to
excellent, or are batts really hopeless?
5. okay, one last thing. To me adding 1" closed cell foam to the inside
face of the OSB sheathing does more good than harm, because it raises
the temperature of that first semiimpermeable surface. That is, the
inside face of the foam is much warmer than the inside face of the OSB
without the foam, which should reduce the condensation potential in the
cavity in winter. Therefore adding the foam should make the assembly
perform better. Am I missing some important factor though? Should I be
leery of 1" of closed cell foam on the inside of the OSB?
Just asking for the moon,
Thanks,

Doug
Doug Horgan, CGP

BOWA Builders, Inc.
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