Spray insulation is for heating/cooling and not great for sound.

There are other forms of winterizing like insulating plumbing, sealing door/windows with rubber gaskets, installing storm windows/doors, setting up heat lamps or other supplemental forms of heat in basements, etc.

New roof and windows, insulation etc don't really add much to ARV, but it makes for a better quality asset.

I live in Maryland, and we're pretty well insulated from economic turmoil thanks to our proximity to DC. 

As an example, you can have a brand new HVAC, but if your insulation is 100+ years old, it's going to be an uphill battle.   

And it's still one of the least expensive areas of the state to live in so I think STRs are plausible and fairly insulated from seasonality since we have year round recreation.

All of these duplexes are modular.Some things I have learned:1) Modular homes absolutely appreciate the same as a standard stick especially if you highlight to your lender the performance improvements such as:-Higher R value insulation.

Your inspector better clean up the insulation they leave on the ground though.

Perhaps a bit noisy but, not if you have insulation under them (when installed). :)  Keep in mind, that YES they are more expensive AND, they may actually get small "dimples" in them from hail... it will show (in many not all) forms of metal roofs but that is NOT covered by insurance (cosmetic damage). 

I think the smaller 2-3 bedroom STR's are a little bit insulated though there are some large condo projects going on as well.