I do have a small access panel I took down to get access to a pipe we can also put back up and that may not hep a ton but a bit."

This is a mother-in-law / guest wing of a custom built passive home (self sustainable from solar,high efficiency electric/insolation) very pretty, and feels like you are in the country for sure with some mountain views on the clear days.

But, you may only be able to have .5-1" under R-panel type, again... all dependent on the situation there. 

The only thing still original is some of the framing, the exterior stucco, the electric panel, the furnace, and the plaster walls and ceiling in the living room.  

With a panel and everything else it can be a quick $6,000. 

@David Yu We completed a full renovation on a SFH this month and had major electrical issues (no grounds, loose boxes, unlabeled panel, two prongs, etc.).

$5,000 - remove wall$1,000 - paint kitchen cabinets$3,000 - paint $1,000 - remove paneling, repair drywall$1,000 - new light fixtures and bathroom fixtures$2,000 - new countertops$2,000 - new appliances$6,000 - new flooring (laminate, carpet, tile)$1,000 - new garage door$1,000- paint siding$3,000 - contingencyTOTAL Rehab - $31,000Those are just things that are obvious from the pictures.

The surplus goes to a repair escrow for now (eventual replumb/rewire) but I'm hoping to go solar within the next 5 years and increase the rents to include solar electric.

Installed new kitchen with granite countertop, new roof, new LVP flooring throughout, upgraded electric panel, and new paint.

Then because it would be new construction at that point, you have to factor in new construction guidelines like fire sprinklers, solar panels, rain barrels, etc.It would probably not be worth wild from an ROI standpoint.