We have recently brought a 60yo stucco house (in Ch-Ch) and are intending to undertake a major makeover. We like the location (hills) and style, so rebuilding isn't an option, plus the framing and foundations are sound.
The windows will be the first to go, replacing with either IV68 timber (Eurovison cedar frames) or uPVC (NK Windows).
The issue is then the patching of the plaster around the new windows (current ones are flush finished to the plaster) plus the extension and moving some windows.
In order to improve the wall insulation from zero we were planning to remove the 1" stucco and 1" timber sarking and replace with 50mm Hebel (I know it's not real CSR Hebel). However the increase in R-value for the wall components outside the framing (Hebel v existing stucco) wasn't much, about 0.25.
Soooo, instead we are leaning towards leaving the stucco and getting a 10mm skim coat over the repairs and old surfaces to give a uniform surface - the existing surface is that splatter gun finish and getting the R-value increase by using the 50mm Kooltherm rigid phenolic board from Forman/Kingspan on the inside (with a 10mm GIB board as well). This will give us an increase of R-value of about 2.0 over the Hebel option.
The big advantage is that we can do all the internal work ourselves, however we're not sure about the required thickness of the new plaster, plus the additional load on the framing and foundations.
Any comments on the phenolic board and / or plaster overcoating?

A few years back I did a major makeover on a stucco house of a similar vintage to yours, and when replacing the windows there wasn't any damage to the stucco as basi
cally we put facing boards around the windows, with a compressable foam strip behind the facing boards, thus hiding the gap. Our local council had no problems with this. As an aside, we completely gutted the house, and put in wool insulation in walls and ceiling and it was nice and warm. My wife and I completed this before I found out a bit more about energy effciency materials/methods. We had a heat pump in the living room and it heated up the house quicksmart.

Am assuming a timber floor for the house? Obviously that would need quite a bit of attention to match your proposed plan for the walls/windows.

If I were doing your house I would be tempted just to stick your pink batts/ wool batts etc in the framing and forget replastering/phenolic board. You could achieve this by either taking off the plasterboard inside, or taking stucco off outside ( then you get to choose the cladding of your choice, not restricted to stucco). I know a lot of people who say taking cladding off is easier - keeps insied liveable during work, and would allow you to change cladding, or at the very least include a air barrier board (ply/hardies) to stop windwash on any batt insulation in your wall space - although this wouldn't be a problem if you just had phenolic board.

Just thinking this through would have batts in the framing space with the phenolic board on the inside of the studs, or would you cut it all up to fit between the studs? If you had batts in stud work and then foam on inside would there be a problem with having a vapour barrier in the form of the phenolic board on the warm side of the house - - hoping for some help from someone else.

Please excuse my rambling post - hopefully there is something of use in there!

Tim