Should interest rates ever get back to any sort of market-driven interest rates, the house of cards could easily finally crash as many have predicted.The mortgage market is very undeveloped in Colombia, whereby prices are purely driven by supply and demand as they should in a modern capitalistic economy.

I am definitely emphasizing the modern conveniences my cabins offer (wifi, full kitchen, delivery services etc) so people feel like they'll have all the comforts of home while still getting a change of pace.  

If you're planning to hold long term, you should look not just for cash flow but also strong economic/demographic trends, modern/diverse industries and low property tax rates.

Added modern features/paint What was the outcome?

Sure, some modern building methods are far superior to what was used in the past, but lots of building methods used today aren't nearly as robust as in prior generations (ask an experienced GC). ....Additionally, a new house is still in its "growing pains" phase, and a lot of serious problems can emerge in the first few years of ownership--e.g.; foundation/structural settling, improper water diversion systems creating rot, etc. 

One of my apartments are up to date and modern.

If it were mine, I would (probably) make the interiors up-to date modern so that it is not super obsolete looking in 10 to 15 years.I would do them as they turn--one unit at a time--and spread the financial hit out over time (both the added turn time and the added out of pocket).I would also check the water heaters for age (service life) too, as well as doing any electrical upgrades when the walls are open (adding additional GFCI outlets or etc...)My rational about this is would be, can the place get market rate rent simply by painting over the paneling (which seems low end to me), and what is the close in competition offering and getting in rent?

My parents refinanced and brought their mortgage rate down to 2.50% almost a year ago and used the funds to completely renovate our kitchen to increase the value on the home and bring a more modern feel to it. 

Minimalist and modern.

Also, join this community https://pacejmorby.com/invite - they have a super active discord which is like a modern text group on steroids. 3.