IMO pulling out fiberglass batt insulation in the walls, that was cut and placed to fit, through some little hole of some sort, won't work (it'll tear) and I'd be tempted to kick that guy in the arse for suggesting that. Then blowing in fiberglass, which will not be as tight fitting down the entire wall with electrical boxes, blocking, (& leftover batts) etc as the original install was.

As far as the spray foam, you say you have a "flat foam roof." I take that as polyisocyanurate on the top side with a membrane roof. That is the best place for insulation for a flat roof and provides your moisture/air barrier. The benefit of spray foam is as a moisture/air barrier that fiberglass batts lack and more Rvalue per inch than batts. But if you already have a moisture barrier, sufficient air sealing and Rvalue, what are you looking to improve on?

Thank you guys! You just saved me $3000. :) The contractor was urging me to do this. My energy bills are already low for this house and it’s hard for me to imagine they would go down that much more. I don’t know if I have a membrane, but it’s a foam roof. I also have very long patio overhangs which helps to shield the interior from the sun. Thank you again!!!

I might ask a local energy rater for a second opinion. When you say "low", I am always impressed by what people consider low. A better way to say it would be - I spend $2000 a year on a/c. I suspect you would think that was low (and it is for the age of house and location). But you could still potentially see a return on investment. Not a great one but still.

I personally don't have any idea how 70 year old fiberglass in AZ would look. I really doubt it would be cut well and installed with the best care.

Definitely leave alone the parts that are not damaged

I just blew cellulose over my batts. Blew 1000 pounds in my 1000 sq. ft attic in 4 hours. About $500. More info if interested.

Badabing2 I’d like to know more? What did you use to spray it?

@fixitupchappie I bought a palette of this (link below) from HomeDepot - free delivery plus you get to rent the machine free for one day if you buy at least 20 bags (think it's $75/day rental, not available at all centers - check locally). Machine is a bit large but on wheels, comes with 100' of hose. Need two people - one to load the hopper, one to blow. Very dusty install - use a painter's suit and good mask (like an N95). R-Factor is 3.7 per inch (fiberglass is about R2.5/in). There's a calculator on Greenfiber site (link below) for R-value and sq. feet. Lots of good comments on the HD site and many great videos on youtube. Cellulose is (IMHO) better than fiberglass - better R-value, fiberglass is a carcinogen, recycled product, doesn't support mold, keeps critters out, etc. And you just blow it on top of whatever you have. I did mine a year ago and noticeable improvement in warmth (Central Calif), also some noise reduction too.

In short it's an easy though dusty DIY job, watch the videos, read reviews, and you'll soon be an expert.

https://www.homedepot.com/p/Greenfiber-All-Borate-Cellulose-Blow-In-Insulation-30-lbs-36-Bags-INS765LD/300584221

https://www.greenfiber.com/homeowners

Thanks will have to look into it