One thing lacking is modern attractive styling and quality amenities. 

While "upscale vs old-fashioned" would be a subjective option, it would be great to aggregate data around a timeframe when "big items" were updated, i.e. cabinets and flooring were updated in <1 year, or roof is <3 years old, etc.

I am looking for the best way to find the facts in a timely fashion to make this decision, so if anyone has tried and true strategies or ideas, I am all ears!

If you pay market price than you will have a tough time executing out in a advantageous fashion.

The casita is a gorgeous, modern unit that rents for 1350/mo and the main house is unimproved from purchase and rents for $1850/mo Lessons learned?

If it is a non trust worthy GC you may never see that money again & in less drastic terms you simply want to pay for work as it is finished like you mentioned. 2) You can control them because the 30k will be returned to you & then you will disbursement Payment to the GC in standard fashion. 3) If the rehab costs less you do not have to pay the overage to the GC & do not loose this money.

A full blown war in the Modern era would likely not yield good results any where.As a side note- Soldiers who would get deployed that are single and renting would lead to a spike in vacancies.

Have you made purchases in this fashion before?  

I’m wondering if the ARV would possibly increase with a modern update or if it’s even worth doing the rehab? 

You can hire inspectors or agents to view the property for move-out inspections and then coordinate with Rent Collection:  With modern technology this is all done digitally.